Motion vision is one of the fundamental properties of the visual system and is involved in numerous tasks. Previous work has shown that harbor seals are able to perceive visual motion. Tying in with this experimental finding, we assessed the sensitivity of harbor seals to visual motion using random dot displays. In these random dot displays, either all or a percentage of the dots plotted in the display area move into one direction which is referred to as percent coherence. Using random dot displays allows determining motion sensitivity free from form or position cues. Moreover, when reducing the lifetime of the dots, the experimental subjects need to rely on the global motion over the display area instead of on local motion events, such as the streaks of single dots. For marine mammals, the interpretation of global motion stimuli seems important in the context of locomotion, orientation and foraging. The first experiment required the seal to detect coherent motion directed upwards in one out of two stimulus displays and psychophysical motion coherence detection thresholds were obtained ranging from 5% to 35% coherence. At the beginning of the second experiment, which was conducted to reduce the differential flickering of the motion stimulus as secondary cue, the seal was directly able to transfer from coherent motion detection to a discrimination of coherent motion direction, leftward versus rightward. The seal performed well even when the duration of the local motion event was extremely short in the last experiment, in which noise was programmed as random position noise. Its coherence threshold was determined at 23% coherence in this experiment. This motion sensitivity compares well to the performance of most species tested so far excluding monkeys, humans and cats. To conclude, harbor seals possess an effective global motion processing system. For seals, the interpretation of global and coherent motion might e. g. play a role in the interpretation of optic flow information or when breaking the camouflage of cryptic prey items. Phoca vitulina) to global motion. This study is the first to determine coherent motion detection and coherent motion direction discrimination thresholds in a marine mammal.The ability to see motion is one of the most basic and also one of the most important functions of the visual system. Many adaptive behaviors depend on the detection of motion or the extraction of motion information from a scene Nakayama. Motion Random dot displays were used as these displays allow assessing motion sensitivity isolated from form or position cues  after 264 trials and constantly performed above 75% correct choices from session 12 on. Note that, during pretraining, trial numbers deviating from a multiple of 30 trials result from motivational problems of the experimental animal during some sessions or trials that were added to a standard session due to training aspects.During pretraining, the seal had to learn to indicate the position of one of two displays Figure , that coFor initial coherent motion detection threshold determination, the performance of the seal was averaged over 90 presentations after which the performance had stabilized resulting in a clear psychometric function Figure a. The thIn the following sessions, coherence detection thresholds with varying parameters were assessed in order to test the influence of these parameters on the seal’s performance within experiments and to assess if the seal’s performance increases with experience over experiments. The seal was trained until reaching a low threshold performance in this coherent motion detection experiment.In phase 1 of the coherent motion detection experiment, the lifetime of the dots was varied which could help to determine if seals possess an effective local motion integration system. Dot lifetime was decreased to 500 ms, 250 ms and 125 ms, while all other parameters were kept constant . The threshold at a density of 0.38 dots/deg2 was determined at 9.2% coherence. At dot densities of 0.77 dots/deg2 and 1.54 dots/deg2, the seal’s coherence thresholds fell to 4.7% coherence . In all eight sessions thereafter, the seal’s performance always exceeded 86% correct choices . The psychometric function obtained during data collection in this experiment is shown in Figure This experiment was conducted in order to eliminate a possible secondary cue that might have guided the seal’s performance in the first experiment, the differential flicker of the positive stimulus. The experimental procedure was changed in a way that now the seal had to discriminate the direction of coherent motion. The seal was viewing one display with either leftward or rightward stimulus motion and had to indicate stimulus motion by moving its head to the left or right respectively. Thus flicker at both sides of the stimulus display area was the same irrespective of stimulus movement. Testing the seal initially with a dot density of 500 dots/stimulus area, a dot lifetime of 1000 ms, and a coherence of 80%, it turned out that the seal was able to adapt to the new experimental condition within one session reaching 86.2% correct choices  with previous experience with psychophysical test procedures served as experimental subject. The seal’s daily diet consisted of 2–4 kg of herring supplemented with vitamins and was entirely fed during the experiments. Experiments were conducted in a freshwater pool with a capacity of 300 m3 and a maximum depth of 1.7 m. The experiments were carried out in accordance with the current German law on the protection of animals.The study was conducted at the Marine Science Center, Cologne, Germany. One harbor seal  was installed in the experimental pool, which accommodated the test apparatus  linked with the projector over a digital visual interface. Random dots displays were designed with a self-written program written in C language in a MS Windows environment using commands of the Open Graphics Library (OpenGL) and the Graphics Library Utility Toolkit (GLUT).2 and 100 cd/m2 depending on dot size. The speed of the dots was almost the same in all experiments. However, since we worked with a plane screen and large display areas subtending up to 80 deg of the horizontal visual field in some experiments the speed of the local motion signals varied between 5 deg/s and 10 deg/s depending on their position in the visual field of the animal. The self-written program computed and stored the actual rate at which the frames were rendered by the graphic hardware for adjusting the timing of the stimuli to the frame rate. Correct timing of the displays was confirmed by a photosensitive cell measuring the lifetime of individual dots. Depending on experiment, dot density was varied from 100 to 1000 dots per stimulus display area corresponding to dot densities of 0.15 dots/deg2 to 1.54 dots/deg2, and dot lifetime was set to 125 ms, 250 ms, 500 ms or 1000 ms.An overview of the stimulus configurations used in experiments, conducted in the order of listing, is depicted in Table 2 (27 deg × 24 deg) each. One area included a coherent motion signal directed upwards overlaid by visual noise (positive stimulus), whereas the other area only contained visual noise (negative stimulus). Noise was programmed as random direction noise  size and the direction of the coherently moving dots was horizontal, either left- or rightwards. Under these conditions, the direction of the coherent motion signal was the only cue for the subjects to rely on, since the pattern of flicker was identical under both stimulus conditions.For the first coherent motion direction discrimination experiment, we used the same principal design of motion signal and noise as in the coherent motion detection experiment, however, we eliminated flicker as a secondary cue. In the coherent motion detection experiment, the subject might have not discriminated the stimuli using the pattern of motion signals the stimuli contained but by the pattern of flicker at the edges of the stimulus areas. Since in the positive stimulus of the coherent motion detection experiment the coherent dots left the stimulus area at the top edge and were reintroduced at the bottom edge, the pattern of flicker created by the disappearing and reappearing dots differed between the two stimuli with the amount of flicker in the positive stimulus being higher at the bottom/top edges than at the left/right edges. To eliminate flicker the test situation was changed such that there was only one stimulus area of 6,400 degN consecutive frames was pN − 1, where p is the coherence or correlation of the display  or the direction of motion was varied between rightward and leftward stimulus motion (coherent motion direction discrimination experiments) in pseudorandom order after Gellermann .


High pressure torsion is known as one of the most popular severe plastic deformation processes. However, it has certain size limitations, especially regarding the thickness of the processed samples. In this contribution incremental high pressure torsion is introduced as a novel severe plastic deformation process. This further development of conventional high pressure torsion is capable of delivering specimens having an extraordinarily high aspect-ratio of thickness to diameter. The features of this process combined with a case-study on a pure copper specimen with a deformed diameter of 50 mm and a thickness of 40 mm is presented. As an important feature it involves considerably high amounts of hydrostatic pressure which inhibits crack-formation during deformation and leads so to almost no limitation in the applicable strain. Consequently, this technique also allows SPD of intermediate and high strength starting materials, such as steels and tungsten t, to diameter, d, shortly (t/d) of the HPT disk is too large Although this technique should theoretically deliver specimens with strongly inhomogenous microstructures, homogeneity in terms of hardness can be reached along the radius. The reason is the existence of a lower limit of grain-fragmentation after applying a material and processing parameter dependent saturation strain. This leads to the minimum grain size and thereby the highest hardness and strength at low disk radii after employing an appropriate minimum number of rotations. This saturation behavior is an important requirement for achieving large scaled specimens and products with satisfyingly homogenous hardness distributions. Nevertheless, an undeniable disadvantage of HPT has always been the small specimen size. In order to overcome the status and reputation of HPT as an academic curiosity, much effort has been taken over the last years to upscale the process and to increase the sample size, see e.g. This technical extension may increase the application possibilities of materials processed by HPT such as for medical 2For the demonstration of IHPT technically pure copper (99.9%) was used. The specimens used for the deformation process had the shape of a cylinder with a total height of 70 mm and a diameter of 50 mm. Before processing the samples were annealed at 700 °C for 1 h, in order to obtain a fully recrystallized starting microstructure that can be used to distinguish between deformed and un-deformed areas. For that purpose the deformed specimens were additionally etched using a commercially available etching detergent for copper. The IHPT process that will be explained in detail in the following section, was carried out on a hydraulic machine with a load of approximately 400 t. The rotational speed was approximately 0.07 rotations per minute. A quantitative evaluation of the changes in the mechanical properties due to IHPT after deformation was performed with Vickers micro-hardness measurements using a microhardness tester from Buehler (Micromet 5104). The indents were carried out with a load of 300 gf and dwell times of 15 s. The positioning of the individual indents will be explained in conjunction with cross-sections of the deformed specimen. The microstructural investigation was performed with a light microscope from Olympus (BX51) and a scanning electron microscope (Zeiss 1525) using back scatter electron contrast.33.1The most important processing steps of IHPT are presented in 3.2In order to demonstrate the feasibility of this technique a case study on pure copper is presented. For the study technically pure copper (99.9%) was used and two different specimens were produced. The first specimen was subjected to 15 rotations to induce a high amount of shear deformation that should allow for a saturated microstructure along the radius. The second specimen was deformed using the IHPT-principle. At first it was deformed to 15 rotations again as the first specimen. Then, the deformation zone was changed in the axial direction by shifting the deformation zone in the tool and another 15 rotations were applied afterwards. In total this incremental process was repeated nine times or in other words 9 deformation steps were applied. In this way the deformed volume increased with every single step where within one step 15 rotations were applied. During one deformation step the deformation zone had a thickness of approximately 8 mm. The step size between following deformation increments was 4 mm. In this way an overlap of the deformation zones between consecutive deformation steps was guaranteed. As support cylinders disks with a thickness of 4 mm were in use and stacked together to get the appropriate heights, see also the examples in Photographs of the specimens subjected to IHPT are presented in In order to investigate the microstructure more in detail a series of micrographs using light microscopy and scanning electron microscopy is presented in A quantitative evaluation of the change in the mechanical properties due to IHPT after deformation were performed with micro-hardness measurements. The indents were carried out on the metallographic cut of the specimen deformed with 9 deformations steps, as presented in 4A reasonable explanation for the slight decrease in hardness along the axial direction may be based on a temperature rise during the deformation process. It is generally known that SPD-processed structures exhibit a rather poor thermal stability compared to coarser grained materials The maximum hardness in the singly deformed specimen is around the same level as measured on the incrementally deformed specimen regarding the area that was deformed in the last deformation step, see εvM, for saturation in the case of pure metals is around 16–32 A comprehensive inspection of the hardness distribution in εvM, of 16 and an approximate thickness, t, of the deformation zone of about 8 mm and 15 rotations as the number of rotations, n, the critical strain is reached at a radius, r, of approximately 2.5 mm. Hence, from this viewpoint saturation should be expected, which is not the case for IHPT presented here. A more likely reason for the gradient in the radial direction is connected to a strain-rate sensitivity known for UFG-materials When one assumes a minimum strain, A comparison with the maximum achievable hardness using conventional HPT with literature data is a very difficult task as it is widely known that the saturation hardness of the same metal and comparable purity can vary markedly due to the large influence of impurities on the grain boundary mobility and so on the grain size The presented deformation technique IHPT  represents a further severe plastic deformation technique with the intention to upscale the specimen size of bulk-nanostructured materials. Compared with continuous high pressure torsion (CHPT) IHPT exhibits a different deformation path To summarize, a new SPD method, called incremental high pressure torsion (IHPT) was introduced which combines the advantages of conventional HPT and overcomes the limitation of a restricted specimen thickness. As a case study, the process was performed with a pure copper specimen showing an ultrafine-grained microstructure in the entire deformed section of the specimen having a diameter of 50 mm and a thickness of 40 mm. Future work will focus on extending the process to materials having a higher saturation hardness, e.g. alloys, steels and composites. In addition a cooling system will be required preventing additional heating and so temperature rise of the specimen during deformation.


This paper was aimed at investigating the volatility and conditional relationship among inflation rates, exchange rates and interest rates as well as to construct a model using multivariate GARCH DCC and BEKK models using Ghana data from January 1990 to December 2013. The study revealed that the cumulative depreciation of the cedi to the US dollar from 1990 to 2013 is 7,010.2% and the yearly weighted depreciation of the cedi to the US dollar for the period is 20.4%. There was evidence that, the fact that inflation rate was stable, does not mean that exchange rates and interest rates are expected to be stable. Rather, when the cedi performs well on the forex, inflation rates and interest rates react positively and become stable in the long run. The BEKK model is robust to modelling and forecasting volatility of inflation rates, exchange rates and interest rates. The DCC model is robust to model the conditional and unconditional correlation among inflation rates, exchange rates and interest rates. The BEKK model, which forecasted high exchange rate volatility for the year 2014, is very robust for modelling the exchange rates in Ghana. The mean equation of the DCC model is also robust to forecast inflation rates in Ghana. When the general level of prices is relatively stable, the uncertainties of time-related activities such as investment diminish. This helps to promote full employment and strong economic growth. When price stability is achieved and maintained, monetary policy makers have done their job well  inflation rate. The Fisher effect simply explains for example that; if the nominal interest rate is say 50 per cent for a given period, and the predicted inflation rate during that same period is 20 per cent, then the real interest rate is 30 per cent. The movement in short term interest rates primarily reflects fluctuation in expected inflation, which in effect has a predictive ability for future inflation  and DCC  models.A researcher can apply all these models on data series and the best model is chosen based on the performance of the model using a criterion. According to , the application of BEKK and DCC in modelling the conditional variance generally achieved similar results and the difference is negligible.The monthly inflation rates, average monthly exchange rates (cedi to US dollar) and interest rates (lending rate to the public) in Ghana spanning the period January 1990 to December 2013 were used for the study. This means that a total of 288 data points were considered for each variable. The sources of data were the Ghana Statistical Service (GSS) and Ghana Commercial Bank (GCB).The data were analyzed using multivariate GARCH, DCC and BEKK models. The procedure most often used in the model estimation involves the maximization of a likelihood function constructed on the assumption of independently and identically distributed standardized residuals.According to Engle and Sheppard , analyzixt is the return observed at time t. Assuming for instance that the model for a return is given as: xt = μt + εt, where μt = Ε(xt/λt − 1) denotes the conditional expectation of the return series, εt is the condition error and λt − 1 = σ(x : s ≤ t − 1) represent the sigma field (information set) generated by the values of the return until time t - 1. Suppose that the conditional errors are conditional standard deviations of the returns yt. Note that ht and yt are independent for all time t, μt = 0, which implies that xt/λt − 1 ∼ N.Suppose that the stochastic process Conditioning of economic and financial models are mostly stated as the regression of a variable’s present values of the variable on the same variable’s past values as indicated in the GARCH model proposed by (Bolleslev (i)ϕ - the weighted long run variance(ii)p previous lags of squared-innovations multiplied by the assigned weight αi for each lagged square innovation(iii)q previous lagged variances multiplied by the assigned βi for each lagged variance.The GARCH consist of the three terms, these are:Since the variance is non-negative by definition, the process Ht was defined by,  and became known as the BEKK model, which is viewed as another restricted version of the VEC model. It achieves the positive definiteness of the conditional covariance by formulating the model in a way that this property is implied by the model structure. The form of the BEKK model is as:Akj and Bkj a N × N parameter matrices, and C is a lower triangular matrix. The purpose of decomposing the constant term in equation KN2 + N(N + 1)/2 whereas in the diagonal BEKK, the number of parameters reduces to (p + q)KN + N(N + 1)/2. The BEKK form is not linear in the parameters, which makes the convergence of the model difficult. However, the model structure automatically guarantees the positive definiteness of Ht. Under the overall consideration, it is assumed that p = q = k = 1 in BEKK forms of application. The difference between the results of BEKK model and the DCC model is highly negligible.Estimation of the BEKK model still bears large computations due to several matrix transpositions. The number of parameters of a complete BEKK model is  '. Furthermore, assume that the conditional returns are normally distributed with zero mean and conditional covariance matrix xt/λt − 1 ∼ N, zt =  ' ∼ N and In is the identity matrix of order n. Ht.To extend the assumptions in the univariate GARCH to multivariate case, suppose that we have Ht ≡ DtXtDt, where Dt is the diagonal matrix of time varying standard variation from univariate GARCH processIn DCC-model, the covariance matrix is decomposed into Dt matrix is not only restricted to the GARCH described in equation In this work, only the DCC will be utilized.Ht for all t, simple conditions on the parameters are imposed. Firstly, the conditions for the univariate GARCH model has to be satisfied. Similar conditions on the dynamic correlations are also required, namely: β ≥ 0 and α ≥ 0, α + β < 1, Q0 has to be positive definite.If the covariance matrix is not positive definite then it is impossible to invert the covariance matrix which is essential in portfolio optimization. To guarantee a positive definite Ht, that is to say θ = , the following log-likelihood function ℓ can be used when the errors are assumed to be multivariate normally distributed:In order to estimate the parameters of The parameters in the DCC model specified in equation  can be dThe estimation follows the following two steps.Xt matrix in the log-likelihood function is replaced with the identity matrix In, which gives the following log-likelihood function specified in equation  for each univariate GARCH process. Since the variance hit for asset i = 1, 2, 3, … n is estimated for t ∈ {1, T}, then also the element of the Dt matrix under the same time period is estimated.It is obvious that this quasi-likelihood function is the sum of the univariate GARCH log-likelihood functions. Therefore, one can use the algorithm to estimate parameter θ2 =  given the estimated parameters In the second step, the correctly specified log-likelihood function is used to estimate Xt is of interest to maximize. Hence we obtain:From equation , the firVariance targeting is used in the dynamic structure and therefore Figure Figure n is the number of years.The cumulative depreciation of the cedi to the US dollar from 1990 to 2013 is 7,010.2% and the yearly weighted depreciation of the cedi to the US dollar is 20.4% using the formulae in equation  and (12)Multivariate GARCH models are estimated by the quasi maximum likelihood technique. Regression Analysis of Time Series (RATS) 8.3 is a widely used software in estimating MGARCH models as a result of its flexible maximum likelihood estimation capabilities and has advantages over many other software packages on estimating MGARCH models. The optimization algorithm used for the maximum likelihood estimation in RATS is BFGS; proposed independently by Broyden , FletcheTable The estimated DCC model’s unconditional covariance matrix is given in equation :12\documFigure Table The parameters A, B and C in the BEKK model are provided below:Figure Certainly, it is evident that the BEKK model is robust in modeling volatility in the depreciation of the cedi to other foreign currencies.Figure Figure The Vector Error Correction Model and Granger Causality test is used to examine the cause and effect of the inflation rate, exchange rate and interest rate. Johansen test of cointegration among the variables using STATA 12 rejected the null hypothesis that there is no cointegration; a precondition to running the Vector Error Correction model as shown in Table The Vector Correction Model evidence long run and short run causality among the variables after the null hypothesis of both “no long run causality and no short run causality” were rejected. After a pair-wise Granger-causality tests at 5% significant level, the result show that, exchange rate Granger-cause inflation rate but the converse does not. Similarly, inflation rate Granger cause interest rate but the reverse does not.Multivariate GARCH, DCC and BEKK models were fitted to the variances of the data. Both models passed the diagnostic test. The mean equation of the DCC model was used to predict the expected inflation rate and proved to be robust in the short to medium term, similarly, the BEKK model was used to predict the expected exchange rate volatility.These predictions suggest that, inflation rates are expected to increase at a very slow rate in 2014. Also, the forecast of exchange rate volatility suggested that, there is a very high risk of abrupt depreciation of the cedi to the US dollar. This implies that the rates of inflation as well as interest rates are likely to react in the long run to the expected volatility in exchange rate for the year 2014.There was generally positive conditional and unconditional correlation between inflation rates and exchange rates, inflation rates and interest rates as well as exchange rates and interest rates. This implies that there is some evidence that when the general prices of goods and services are stable, interest rates are expected to be stable and possibly low. That of inflation and exchange rates implies that the stability of inflation means that the cedi depreciated to the dollar at low rate. There was evidence that the cedi has depreciated cumulatively to the US dollar of 7010.02% from 1990 to 2013 with a weighted annual average depreciation of 20.4%.The volatility experienced in inflation, exchange and interest rates in the study, to a large extent were not in elections year. It is therefore factually inaccurate to assert that during election years, the cedi depreciates faster to the US dollar. The evidence rather suggests, there seem to be volatility in these economic variables, periods after elections were held rather than during elections year and also during the first quarter of every year.It was also evident that, the fact that inflation rates were stable, does not mean that exchange rates and interest rates are expected to be stable. Rather, when the cedi performs well on the forex, inflation and interest rates react positively in the long run. All things being equal, this reaction tickles down to all aspects of the economy thus, occasioning improved standards of living.The economy of Ghana reacts positively in most instances when the cedi performs strongly on the forex market. Such performance was evidenced in 2003 when the cedi depreciated to the US dollar at an average of 3.81%, during that same year the Ghana Stock Exchange recorded returns on investments of about 155%, the highest since its inception. The success of the cedi during this year could be traced to foreign inflows of HIPC benefits into the country. This implies that the health of the economy of Ghana is highly dependent on the strength of the cedi against foreign currencies such as the US dollar, Euro and the British pound sterling.Recommendations are made for both policy formulation and areas of further research based on the findings of the study.To begin with, it is recommended that policy makers use multivariate GARCH models to study the dynamics of economic and financial data. The DCC model proved to be robust in modeling the correlation among inflation, exchange and interest rates, and the mean equation of the model was robust for modelling inflation rates in the short to medium term. Similarly, the BEKK model was found to be robust in modeling volatility as well as forecasting.Secondly, the research work has revealed that, the health of Ghana’s economy is highly dependent on the strength of the Ghanaian currency: cedi against the foreign currencies since the country is import dependent, as such there must be a national agenda to increase foreign inflows and introduce a policy aimed at Exchange Rate Targeting (ERT). The forecast is also an indication that policy makers and industry players can effectively plan to curb uncertainties in the Ghanaian economy given these models are used.Thirdly, there must be a national consensus to reduce imports into the country by improving production and in the long run increase non-traditional exports. The government could adopt a policy through consensus with private sectors (services) to list on the Ghana Stock Exchange to attract Ghanaians to own shares, tax incentives could be used as a stimulus package. This is to ensure that 100% of the profit is not repatriated. Government could also dialogue with the private sector and propose a policy that mandates foreign owned companies to delay about 50% repatriation of their profit in the economy of Ghana for about two years. Government must also adopt a policy to reduce the number of State delegations to international events abroad to about 20%, this could also reduce the pressure on the Ghanaian cedi.Lastly, a study into the dynamics of interest rates, stock returns and exchange rates is recommended. Other economic indicators such as money supply, balance of payment and budget deficit could be added to inflation rate, exchange rate and interest for modelling using multivariate GARCH models. Modelling the volatility in the five most traded currencies in Ghana is also recommended. Impulse analysis of inflation rates, exchange rates and interest rates is suggested as well.


We aimed to investigate the contemporary usage rate and habits of the WHO Surgical Safety Checklist (SSC) in German urological departments.We designed a 26-item questionnaire that was sent to all urological departments in Germany. The primary aim of this study was to evaluate the usage rate of the SSC. Secondary aims were to compare perioperative characteristics of users vs. non-users of the SSC and to assess circumstances of the SSC application.A total of 213 of 234 (91 %) urological departments were users of the SSC, and 21 (9 %) were non-users. SSC users had more often a standard protocol, took less time and had fewer people involved for checking perioperative patient data compared to non-users. Financial budgeting for the SSC existed in 55 (24 %) departments and for patient safety in 73 (32 %) departments.The usage rate of the SSC in urological departments in Germany is high despite restricted financial budgeting. Users of the SSC profit by saving time and manpower for checking perioperative patient data.The online version of this article (doi:10.1186/s13037-015-0082-5) contains supplementary material, which is available to authorized users. Surgery is one of the most complex health interventions to be delivered. An estimated 234 million people require surgical treatment every year for different medical reasons , and advThe Safe Surgery Saves Lives Study Group at the World Health Organization published a perioperative surgical safety checklist (SSC) in 2008 . The intThe objective of this study was to evaluate the usage rate of the SSC in urological departments in Germany. Secondary aims were to compare perioperative characteristics of users vs. non-users of the SSC and to assess circumstances of the SSC application.www.surveymonkey.com and was approved by an institutional review board. The target populations were the urological departments in Germany. Email and postal addresses of all departments were collected from the database of the German Society of Residents in Urology. Since the number of 332 departments was reachable for this survey, there was no sampling done. The study was conducted in accordance with the Ethical Issues in Patient Safety Research published by the World Health Organization.The survey was designed and conducted according to reporting guidelines for surveys found on equator-network.org, an international initiative providing robust reporting guidelines , 10. TheBefore administration, the survey was tested for usability and technical functionality by doctors from the investigators’ department. It was then sent out to the 332 urological departments via email containing the web link to the online-survey. Once the survey was started an answer to every question was mandatory until completion. The timeframe for data collection via email distribution of the survey was 2 weeks. In order to increase the response rate, the survey was printed out and sent to all 332 urological departments as a paper version. Enclosed was a note not to fill out the paper survey if the online version had already been completed. The timeframe for data collection via postal distribution of the survey was 8 weeks.2 test was applied. The Mann–Whitney U-test was used to assess differences concerning how many people were engaged in and how much time was consumed for checking perioperative patient data. A p-value of less than 0.05 was considered significant.Statistical calculations were performed using Statistical Package for the Social Sciences 22.0 software . The groups of users of the SSC and non-users of the SSC were compared with regard to different parameters. To test whether a standard protocol for checking perioperative patient data was used more frequently by users of the SSC or by non-users of the SSC, the χOverall, 234 of 332 chairmen responded to the survey resulting in a response rate of 70 %. Of these, 119 (36 %) responded to the online version and 115 (35 %) to the paper version of the survey. Of the 234 responders, 213 (91 %) were users and 21 (9 %) were non-users of the SSC. The users of the SSC found it reasonable and not very laborious (79 %) rather than reasonable and laborious (19 %) or unreasonable and laborious (2 %). The estimated time consumption for completion of the SSC is shown in Fig. p = 0.001). In addition, checking perioperative patient data took less time (p < 0.001), and fewer people were involved (p = 0.008) in the user group than in the non-user group. The reason for non-usage of the SSC was seldom for financial (10 %) or acceptance (24 %) matters and remained unclear (24 %) or of other nature (43 %) in most of the cases.Differences found between the groups of users and non-users of the SSC are listed in Table Figure A survey on the use of the SSC was sent out to all urological departments in Germany. The results of a representative sample showed a high, but incomplete, usage rate of the SSC of 91 %. The users of the SSC needed less time and fewer people to check perioperative patient data than the non-users. An improvement of the SSC through adaptation to specific procedures in minimally invasive and prosthetic urological surgery was found to be useful by the majority of departments.The usage rate of the SSC was 91 % in our series of urological departments in Germany. Recent surveys reported a slightly lower usage rate in Switzerland of 79 %  and in IAlthough the usage rate of the SSC found for urological departments in Germany was high this does not automatically go along with compliance to the SSC, which represents an unresolved conundrum in the current age of safety checklists. A recent prospective observational study of 854 surgeries performed in Colorado revealed a uniformly poor compliance with respect to assessment of case duration, blood loss, anesthesiologists’ concerns, or display of essential imaging . MoreoveThe time consumption for checking perioperative patient data was lower for the group of users of the SSC than for non-users. Our results of an average time consumption of less than 2 min for completion of the SSC are in agreement with the time consumption found by Taylor et al. . MoreoveOnly 32 % of departments had a financial budget for patient safety, and only 24 % had a budget for the SSC. In this context, the question of cost effectiveness of the SSC must be discussed. Costs of implementing a checklist mostly involve checklist development and modification, formal staff notification, training, and additional operating room time. In 2010, Semel et al. performed a hypothetical decision analysis of the checklist introduction . Per-useDespite the described success of the SSC, there is still much to be improved. Since every specialty has its own specific needs, the adaptation of the SSC to urological conditions was considered useful by 63 % of the departments. An example for adaptation of the SSC was presented by Khan et al. who developed a comprehensive checklist to be used in operating theatres with advanced robotic technology . The SSCThere are some limitations to the findings of our study due to survey methodology. Although the response rate of 70 % was very high for a survey, the findings might not be representative for all urological departments because 30 % did not respond. We assume that users of the SSC tended to answer the survey more frequently than non-users, and thus the real usage rate of the SSC might be slightly lower than 91 %. Furthermore, there is the potential for a double answer from one department for both the online and the paper version of the survey, which were sent out successively. However, the paper version included a note not to fill out the paper survey if the online version had already been completed. Finally, our survey was limited to the use of the SSC and did not monitor the compliance to the SSC in terms of quality and performance level of adhering to all required steps in the protocol.We found a high usage rate of the SSC in urological departments in Germany of 91 %, although these departments often lack a budget for the SSC and for patient safety. Users of the SSC found it reasonable and saved time and manpower for checking perioperative patient data compared to non-users. The checklist should be understood not merely as a list of items to be checked off, but as an instrument for the improvement of communication, teamwork, and safety culture in the operating room, and it should be used accordingly.


We show the positivity or negativity of truncated correlation functions in the quantum XY model with spin 1/2 (at any temperature) and spin 1 (in the ground state). These Griffiths–Ginibre inequalities of the second kind generalise an earlier result of Gallavotti. Correlation inequalities, initially proposed by Griffiths , have beIn his extension of Griffiths’ inequalities, Ginibre proposed a setting that also applies to quantum spin systems . The goax. We consider the hamiltoniana . The second inequality is perhaps best understood classically; if the first component of the spins increases, the other components must decrease because the total spin is conserved. Corollary entclass1pt{minimaThe case of higher spins,  in Eqs.  and  correlations.The proof is straightforward algebra. Notice that both terms of the right side have There exists an orthonormal basis on As a consequence, there exists an orthonormal basis of For for by Lemma . This isThe second inequality (with This section is much more involved, and our result is sadly restricted to the ground state. Our strategy is inspired by the work of Nachtergaele on graphical representations of the Heisenberg model with large spins . We consmentclass2pt{minimIt is perhaps worth noticing that the tensor products in this section play a different rôle than those in Sect. a in the Gibbs state with hamiltonian We introduce the new lattice It is useful to rewrite The Hilbert space at a given site, A, and singlet on Let The ground state energy of B such that It follows from this lemma and Eq.  that alla, we show thatc large enough so that all eigenvalues of We actually prove the result for the hamiltonian  and the given by , is a prOne can replace equality  in the snt}σ1 in , and \doWe can assume that for any mentclass2pt{minim


Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength. A faster alternative to switching using magnetic field pulses was demonstrated by Stanciu et al.0 FePt. Until now all-optical control of the magnetisation had been confined to ferrimagnetic materials and these ferromagnetic materials exhibit high uniaxial anisotropy important for magnetic recording and other magnetic nano-technologies. The underlying physics of TIMS was investigated by Barker et al.Further investigations have shown that a wider range of transition metal - rare earth alloys and synthetic ferrimagnetic materials exhibit all-optical switching in some manner8et al.et al.et al. claims it is within the range given by theoretical estimations. Since continuous films behave in a qualitatively different manner to granular ones and the larger uniaxial anisotropy in FePt would suggest that the all-optical switching mechanism remains unclear in these types of ferromagnets.The role of the inverse Faraday effect in switching a continuous Co/Pt system was investigated by Cornelissen 0 FePt for comparison with the experiments of ref. 1360 FePt15In this report we explore and compare two possible mechanisms for helicity dependent switching in ferromagnets; first the inverse Faraday effect and second a thermal ‘reptation’-like effect. We concentrate specifically on L10 FePt using the Hamiltonian derived by Mryasov et al.20mz = 0 plane is monitored. The large anisotropy in L10 FePt is sufficient that, despite this short timescale, the magnetisation will then relax to the easy axis after the laser pulse. This is repeated 20 times to provide the probability of the grain switching from its original orientation into the reversed state.The inverse Faraday effect has been long been suggested as a mechanism for helicity dependent all-optical switching but despite various theoretical treatments2172 and (b) 14 mJ/cm2. There is a clear region of deterministic switching for high field strength and long duration for both fluences. However for a 10 T field magnitude a duration of approximately 0.6 ps is required while for a large 60 T field this is only reduced to approximately 0.2 ps. This represents the opto-magnetic field remaining in the material in the range of 2 to 6 times longer than the pulse width at magnitudes which are hard to produce externally. With low field magnitude and duration the field is not sufficient to cause consistent switching but there is still a possibility of switching caused by thermal fluctuations yielding a thermally demagnetised film for sufficient laser fluence. Comparing (a) and (b) we can see that the increased fluence has not improved the switching window but rather the enhanced thermal effects causes a more randomised final state. This can be seen as in the low magnitude-short duration regime the probability of remaining unswitched is reaching 50%.The switching phase space, expressed as the percentage of unswitched grains, is shown in et al.et al. conclude that the IFE is a viable explanation for all-optical switching in ferromagnets but do not consider further mechanisms.This switching window is similar to that seen by Cornelissen It is clear that the inverse Faraday effect modelled in this manner may give rise to the observed optical switching but it is also clear that thermal effects can dominate. The effect of the laser heating is to quickly demagnetise the grain within a few hundred femtoseconds but then the re-magnetisation process is on the time-scale of picoseconds2, the ratio KV/kBT is large and essentially the switching probability is zero. Above ≈ 8 mJ/cm2 there is a possibility for the grains to switch direction and the probability increases strongly with fluence until about 14 mJ/cm2 where the peak electron temperature is high enough to fully demagnetise the grain. At this point the grains would be evenly distributed between up and down and so the probability of switching would be 0.5. Beyond 16 mJ/cm2 both the electron and phonon temperatures remain above the Curie temperature on a much longer timescale governed by the cooling rate of the sample. The effect of a constant applied field is to provides a bias to the energy barrier and thus decreases or increases the switching probability depending on whether it is oriented parallel or anti-parallel to the starting magnetisation.To understand the role that thermal effects play we now investigate the switching probability during a single laser pulse without any opto-magnetic field as a function of the laser fluence. Ps ≠ 1) the mechanism will not lead to the exact switching of that grain. Therefore we need to consider an ensemble of grains to observe the final magnetisation. In an ensemble the mechanism is as follows. The laser heats all the grains, but those grains with a magnetisation oriented in the higher absorption direction will achieve a higher temperature with consequently a relatively large switching probability according to This dependence of the switching probability with absorbed laser fluence describes a simple mechanism for all-optical switching. If the absorbed fluence depends on the relative orientation with respect to the laser helicity then there will be a difference in the switching probability and thus a net probability of ending in a specific orientation. Since the thermal switching probability is not deterministic  is the probability of the grain switching by a single laser pulse and δ± = 1 ± Δ/2 is a factor describing the difference in the absorbed fluence due to the magnetic circular dichroism. Δ is the MCD ratio, which is of the order of a few percent. For a detailed parameterisation of this model the switching probability is taken to be that found using the atomistic spin model in where n+ + n− = 1, we findIn equilibrium the states will satisfy detailed balance and the using the conservation of the total probability, This shows the net magnetisation reached after an sufficiently long series of laser pulses. In essence this relies on the relative difference in the transition rates which can be non-zero even at very low laser fluence but may take much longer to reach.Solving with the switching time given byτ, is shown in τ+ and τ− over a range of fluences. τ shows no variation with different MCD ratio while τ+ and τ− show a widening separation for larger MCD, here only a relatively large MCD ratio of 5% is shown. The switching times drop significantly with fluence since the probability of switching shown in The switching time, et al.m(0) = 0, it is easy to show that the gradient for a small number of laser pulses isP(Fδ+) − P(Fδ−) which, along with the single shot switching probability, either from experiments or atomistic calculation, can be directly related to the MCD value; potentially an important check on the validity of the model.This shows that over a small number laser pulses the acquisition of magnetisation is essentially linear building up after each step. m∞. Below a critical value of fluence, no acquisition of the magnetisation occurs, essentially because the laser heating is not sufficient to induce thermally activated transitions over the energy barriers. A weak dependence of the critical fluence with MCD ratio may be expected since the high absorption orientation may absorb sufficient energy to become thermally active but since the MCD ratio is small the central fluence needs to be large. Above the critical fluence the behaviour is non-monotonic, exhibiting a rapid increase resulting from increased thermal activation. At a fluence of around 9.5 mJ/cm2, independent of the MCD value a peak is reached, after which the magnetisation decreases due to the increasing thermal instability at elevated temperatures.The net magnetisation caused by the thermal switching is shown in et al. states that the magnetisation observed in the sample after the repeated laser excitation is approximately 20% of saturation which in our measurements is reached by a MCD of 3%. The MCD can be estimated from measurements of the polar Kerr rotation in radians which, for L10 FePt with a 800 nm laser, appears to be approximately 0.87%et al. measure a MCD of 1.5% in GdFeCo and also demonstrate that it can be increased by tailoring the structure of the multilayer sample increasing up to 3%. This implies tailoring the sample would be a possible route in increasing the magnitude of the thermal switching effect.Whilst this simple model is unlikely to give quantitative results it does show that even a small MCD will give rise to a measurable net magnetisation over a series of laser pulses. The maximum net magnetisation is close to the steepest gradient of the switching probability but due to the thermal randomisation at high fluences it is not centred on the steepest part. The magnetisation in et al. where a 700 Oe field could eliminate the all-optical switching. The slight difference in the field strength indicates that the true MCD value of the system is less than 2%. et al. observe, the increase in the field strength improves the saturation for σ+ but for σ− it reduces the saturation until it fully counters the optical switching at 0.1 T.The effect of an applied field is to bias the thermal switching probabilities, as shown in et al.Finally we consider the effect of the helicity of the laser pulse on the evolution of the magnetisation starting from a state of full magnetic saturation. The results are given in 0 FePt media has been investigated considering two alternative mechanisms. Firstly, switching triggered by a combination of elevated temperatures and an assumed opto-magnetic field induced by the inverse Faraday effect has been investigated. By using atomistic spin dynamics parameterised from ab initio calculations the switching window is seen to require fields that are either of magnitude in excess of 60 T or a duration greater than 5 times that of the laser pulse. Such large fields are perhaps justifiable for a 2-sub-lattice ferrimagnet such as GdFeCo, where switching is driven by a 2-magnon bound stateIn this study, the underlying physics of optically induced switching in L1et al. is that of an optically-induced reptation. The thermal activation during the demagnetisation caused by the laser allows the grains to switch, and if the different orientations absorb different amounts of energy from the laser due to the MCD effect then there is a difference in the transition rates. In a simple 2 state Master equation approach, using single-shot transition probabilities determined by the atomistic model, these different transition rates are shown to give rise to an net magnetisation over repeated cycling of the laser. An MCD of 3% is sufficient to induce a magnetisation similar to that seen experimentally. The effect of an applied field is to bias the transition probabilities and which then inhibits the reptation effect when it is parallel to the magnetisation of the high absorption state or aids it when in the opposite orientation. This model of the helicity dependent all-optical switching in FePt seems physically justifiable and requires only the assumption of an MCD value of Δ ≈ 2%. However, it does not exclude the IFE from playing some role in the switching but importantly it removes the necessity to invoke the unreasonably large opto-magnetic fields required for the IFE to be the dominant mechanism. Finally, we have shown that optically-induced switching over a series of laser pulses, the optical reptation effect, is a new mechanism distinct from TIMS in granular ferromagnets. Although the effect is relatively weak, as found experimentally by Lambert et al.A simpler explanation of the results presented by Lambert Atomistic spin dynamics models the magnetic material as Heisenberg  spin moments that are localised to the atomic sites. The ensemble of spins are modelled by the time integration of the Landau-Lifshitz-Gilbert equation:i = μi/μs are three-dimensional reduced magnetic moments of unit length and the effective field is λ is the atomistic damping (coupling) and ξ is a stochastic thermal noise term which is used to keep the ensemble at a finite temperature. The thermal noise is a Gaussian white noise process with the following mean and variance:where the St = 1 × 10−16 s. To accelerate the dynamics the model is implemented on graphics processing units (GPUs).To integrate the coupled equations of motion the semi-implicit method is used260 phase using an effective spin Hamiltonian which was constructed by Mryasov et al.FePt is modelled in the ordered L1Jij  which is represented in the second sum.The first sum represents the Heisenberg exchange energy of magnetic moments and contains both an isotropic exchange and two-ion anisotropy component that are not restricted to nearest-neighbour interactions. Consequently the exchange interactions Te, and lattice temperatures, Tl, are governed by the following equationsThe effect of the laser is incorporated using the two temperature modelCe and Cl are the electron and phonon heat capacities respectively and Gel the electron-phonon coupling constant. P(t) describes the laser heating power which has a Gaussian shape centred at t0 with the pulse width τl = 100 fs. The fluence, F, is coupled through a material specific constant I0. Parameters for granular FePt are given by Mendil et al.where et al.E, asTheoretical treatments of the inverse Faraday effect predict that the interaction of the polarised light with a magnetised media will create a magnetisation or magnetic field within the media3ε0 is the vacuum dielectric constant and α is the coefficient of the magnetisation linear term in the expansion of the dielectric tensor εij. The direction of the field is either parallel or anti-parallel to the propagation direction, depending on the helicity, and so we consider a perpendicular set up where this is along the film normal, i.e. where hIFE and td = t1 − t0 are the magnitude and duration of the IFE field respectively. t0 and τl are the centre and pulse width of the laser in the same manner as used to model the heating effects of the laser.where To parameterise the two state Master equation the probability of a single grain switching is calculated using atomistic spin dynamics. The results are shown in P∞, F0 and ΔF as fitting parameters. With no external field the effect of a sufficiently high fluence will be to demagnetise the grain completely and as F → ∞ the grain will have an equal chance of entering either orientation meaning P∞ = 1/2. With a constant external field the switching will be biased but thermal effects mean that not all of the grains will align with the field as the system cools implying that P∞ for H ≠ 0 will only tend to 1 for high fields. Since fitting was done for zero field and ±1 T to model the effects of a smaller field a linear interpolation of the constants in with How to cite this article: Ellis, M. O. A. et al. All-optical switching in granular ferromagnets caused by magnetic circular dichroism. Sci. Rep.6, 30522; doi: 10.1038/srep30522 (2016).


It is found that the lattice structure and crystalline morphology of CaCO3 can be tailed by the electric field applied to the solution during its crystallization. The calcite structure with cubic-like morphology can be obtained generally without electric field, and the vaterite structure with the morphology of nanorod is formed under the high electric field. The vaterite nanorods can be piled up to the petaliform layers. Both the nanorod and the petaliform layer can have mesocrystal structures which are piled up by much fine units of the rods with the size of several nanometers. Beautiful rose-like nanoflowers can be self-arranged by the petaliform layers. These structures can have potential application as carrier for medicine to involve into metabolism of living cell.The role of electric field is investigated in determining the structure, morphology, and crystallographic characteristics of CaCO Electric field is ubiquitous in nature. It causes the phenomena as great as thunder and lightning or even as fine as the electrostatic interaction among atoms or molecules. It was proposed that the earliest organic compound to biomolecule was produced in the ancient sea on the earth under high electric field, i.e., thunder and lightning . The car3 is one of the standard model systems because of its abundance in nature, participation in the formation of a certain geologic structure as Karst cave, association with biological calcium metabolism, its important industrial applications. Crystallization and morphological control of CaCO3 have attracted extensive attention for decades [3 nanostructures synthesized under the high electric field from solution is investigated and found that they are much different from those without electric field.CaCO decades –23. Much2  was dissolved in 10 ml absolute ethanol  and then transferred into a syringe as injecta. 2.76 gK2CO3  was dissolved in 200-ml deionized water in a stainless steel vessel as a base solution. The vessel was linked to the ground of high voltage power serving as a counter electrode. The syringe was fixed on the ejector jet pump. The syringe nozzle was linked to a perfusion tube, which the other end was fixed on an entry needle. The entry needle simultaneously served as an electrode, to which a high electric field of 0–1000 kV/m can be applied, and the distance to the counter electrode is 10–25 cm in our laboratory systems. The injecta solution was injected into the base solution which was stirred quickly by magnetic stirrer. In our experiments, 0 and 8 kV were employed and perfusion flow was fixed at 80 μl/min. After the completion of the perfusion, obtained white slurry was filtered and washed several times by deionized water. Through the vacuum drying, the white as-prepared powders were checked by the X-ray diffraction , field emission scanning electron microscopy , and transmission electron microscopy .The synthesis system is illustrated in Fig. 3 has three anhydrous crystallographic polymorphs: vaterite (the least stable), aragonite, and calcite (the most stable). Vaterite particles do not show well-defined morphologies and usually aggregate into spherical particles. The vaterite form can crystallize in either an orthorhombic or a hexagonal structure. With the aids of surfactants and/or templates, hollow vaterite spheres, micro floret, hexagonal prism vaterite crystalline powders, etc. could be synthesized. There is seldom aragonite in nature. It may be associated with the activity of the creatures on the earth. Among the three polymorphs of CaCO3, calcite would be crystallized generally from the solution without outside disturbance because it is the most thermodynamic stable phase.CaCO3, two comparable experiments have been done. In our study, both the precipitation of CaCO3 chemical reactions under 8 kV (~800 kV/mm) electrical field and that under electrical field free (0 kV/mm) were completed in our instrument as described above and named as electric field (EF) sample and electric free (NE) sample, respectively. The XRD patterns are shown in Fig. To clear investigate the effect of electric field on the crystallization of CaCO3 can be identified by the Raman spectrum, and the fine distinction on phase structures can be distinguished [3 crystals [−1 overlap, but vaterite has double peaks whereas calcite has mono one. The most intense Raman bands are observed in the low frequency region (50–400 cm−1), which corresponds to the lattice mode vibrations. In these bands, the characteristic peaks of calcite are strong and narrow, whereas the vaterite bands are large and overlap at 150 and 281 cm−1 with calcite. The modes of wide band around 110 and 300 cm−1 are the characteristic vibration of vaterite lattice as shown as Fig. The vibrational spectroscopy as Raman spectroscopy is sensitive to the structural transformation; the distortions and defects of lattice cell at the molecular level can be detected . It is anguished . It is acrystals –29. Figucrystals , 29. TheThe microstructures of EF sample by SEM are shown in Fig. The microstructures of NE sample are shown in Fig. In order to study the characteristics of the crystallization under the electric field, more details of the sample EF was observed by TEM. Figure It is amazing when we check the SEAD of the sample. A series of perfect hexagonal single crystal diffraction pattern is revealed in Fig. 3 under the electric field are described in Fig. 3 from solution under electric field is illustrated in Fig. Polarized hydroxyapatite ceramics was used to study the effect of surface electric field on crystallization of calcite. It was found the oriented growth of calcite crystals with the rhombohedra {10.4} plane parallel to the polarized hydroxyapatite substrates on both negatively and positively charged surfaces due to the electrostatic force applied to the precipitated ions which accumulated on the surface of the substrates . The eleTo understand the transition between different polymorphs further, density functional theory (DFT) methods can enable itself as an extremely powerful tool for elucidating the energy changing of different polymorphs under electric field , 34. The3 from solution. The calcite structure with cubic-like morphology can be obtained usually during deposition from solution. On the other hand, the vaterite structure with morphology of nanorod is formed under the high electric field. During crystallization of vaterites nanostructures from solutions, the electric field splits the titrant to nano-beams and provides an electrical field to make ions orientation in solution and thus changes the crystallization characteristics of the precipitations. Both calculation and experiments confirmed that the electric field is propitious to the crystallization of vaterite during deposition from solution. The vaterite nanorods we synthesized under high electric field can be self-arranged into beautiful rose-like nanoflowers. The petal of rose-like nanoflowers is detected as mesocrystal, in which crystalline structures are constructed and/or transformed from larger units instead of single ions. Therefore, crystals can be assembled from nanoscopic building units in an almost perfect three-dimensional orientation to form so-called mesocrystals, exhibiting well-faceted outer surfaces.The electric field can be one of the most important facts to determine the polymorphs and morphology of the materials during their synthesis and their crystallization. It is found that the lattice structure and crystalline morphology can be tailed by the electric field which applied to the reaction system during deposition of CaCO


Identification and preservation of the marginal mandibular nerve (MMN) remains an important step in otolaryngology procedures. Current publications place the MMN at least 1 cm below the mandible. This study will evaluate the accuracy of the method of determining the surgical location of this branch of the facial nerve in vivo.MMN were examined in 52 consecutive otolaryngology patients. Using a validated landmarking scheme, distances were measured from the inferior edge of the mandible and the lowest point of the nerve. A comparison of 33 nerves pairs was undertaken. Effect of patient’s age was analysed.Eighty five nerves were landmarked. The mean position of the nerve was 0.2–3.4 mm higher than the margin of the mandible. There were no significant difference in position with respect to age and left versus right comparisons.The marginal mandibular nerve (MMN) is significantly higher than previously published. The location of the nerve on the right does not correlate with the left. Location of the nerve does not correlate with patient’s age. The facial or VII cranial nerve is a mixed nerve composed of both motor and sensory branches and is responsible for the motor innervations of facial expression muscles, lachrymal secretion and partial control of the gustatory sensation . The facIdentification and preservation of the marginal mandibular nerve remains a critical step in otolaryngologic, cosmetic and oncologic head and neck surgery. Iatrogenic injury to the marginal mandibular branch (MMB) during surgery of the neck often results in disorders of facial expression and has been an important reason of medicolegal actions . Injury The marginal mandibular branch supplies the muscles of facial expression that pull and close the angle of the mouth and pulls the lower lip downward (depressor labii inferioris and depressor anguli oris). The nerve passes along the inferior border of the mandible, often looping down into the neck, deep to the platysma and depressor anguli oris . Touré eDistortion of the position of the facial nerve due to parotid tumors will also affect the position and anatomy of the marginal mandibular branch. Perhaps one of the most challenging situations is associated with a displaced facial nerve in large or vascular tumors. It is important for the surgeon to maintain a hemostatic field to identify the nerve accurately. The marginal mandibular branch is used frequently as a guide to the main trunk of the facial nerve, but clear guidelines for locating the marginal mandibular branch are often lacking .Although the intraparotid anatomy of the facial nerve has been very well documented, the surgical approaches to the peripheral, extraparotid branches of the facial nerve have not been described as accurately. The direction followed by the facial nerve branches beyond their emergence from the ventral, cephalic and caudal borders of the parotid gland up to the facial muscles has been studied by several anatomists, but so far, no consistent description of them has been given .At the University of Alberta, over 350 procedures performed annually that requires the identification of the marginal mandibular nerve. The positions of the marginal mandibular nerve were frequently observed to be higher than the published literature. So our hypothesis was the marginal mandibular nerve is located significantly higher than previously published. The objective of this study is to assess the position of the marginal mandibular nerve in relation to the inferior border of the mandible.The study was approved by the human research ethics board at the University of Alberta, and informed consent was obtained from each patient for use of their data within the prospective in vivo study. Fifty two consecutive patients were enrolled between September 2005–March 2006. Our exclusion criteria were 1-tumor involvement of the submandibular region and/or 2-previous irradiation. We identified 85 nerves. The types of surgeries performed were: oncology/neck dissections (46/52)—88 %, salivary gland procedures (4/52)—8 %, parapharyngeal space (2/52)—4 %  below the mandible Fig. .Fig. 2ReThe measurements of 1-vertical distance from the angle of the mandible (blue arrow) and 2-lowest point of the nerve with respect to the inferior edge of the mandible (green arrow) were obtained . 33 Patients with bilateral measurements.Marginal mandibular nerve location relative to the inferior border of mandible was measured Table . We wereAlso, MM nerve position relative to the test value of 10 mm below the mandible was measured Table , and we Right versus left comparison relative to inferior border of mandible was done Table . Thirty Right MMN: Pearson correlation coefficient: 0.11. Linear regression of age: p = 0.46 (NS).Left MMN: Pearson correlation coefficient: 0.24. Linear regression of age: p = 0.15 (NS).Correlation and regression analysis of age to lowest position of MM nerve was done Fig. . The ANOThe marginal mandibular branch of the facial nerve can be difficult to locate in the process of performing a neck dissection, or for any procedure in the upper neck. Careful attention to the anatomic relationships is needed to allow safe identification and preservation of this important structure. During a neck dissection, complete clearance of nodal tissue is often required that requires a sound anatomical knowledge of the nerve.Current publications describe the position of this facial nerve branch as “about 1 cm in front of and below the angle of the mandible” , then “tNelson and Gingrass  noted thThe observation by Baker and Conley  that theZiarah and Atkinson  dissecteIn a study by Dingman and Grabb , 100 facPotgieter et al.  indicatePeterson and Johnston studied 100 patients undergoing parotidectomy and found that the marginal mandibular branch can be located near the angle of the mandible at a point 4.0–4.5 cm from the attachment of the ear lobe . Baker aIn the present study, we describe the accurate course and localization of the marginal mandibular branch by using the ramus of the mandible and facial artery as certain anatomical landmarks. Both of these landmarks can be felt easily by palpation in humans and therefore, they have a practical importance for the surgeon. Marginal mandibular nerve location relative to the inferior border of mandible was measured Table .In our study, the main nerve position in the right side was 2.7 mm above the right angle and 0.2 mm above the right lowest point, while in the left side the mean nerve position was 3.4 mm above the angle and 1.3 mm above the lower point. On the other hand the lowest nerve position in the right hand side was 10 mm below the angle of the mandible and to the lowest point of the mandible as well, while in the left side, the lowest point was 6 mm below the angle of the mandible and 10 mm below the lower point. Also, the location of the highest point of the nerve compared to the angle and the lowest point of the mandible in both sides, which showed that in the right side the highest point is 20 mm above the angle of the mandible and 13 mm above the lowest point of the mandible. In the left side, the highest point was 13 mm above the left angle and 10 mm above the lowest point of the mandible. The mean difference of the position of the MMN and the angle of the mandible and the lowest point of the mandible to the right angle 12.723 mm, to the right lowest point is 10.149, to the left angle is 13.395 mm, and to the left lowest point is 11.342 mm. The p value was <0.001 . Also, the 95 % confidence interval (CI) in relation to the four points showed 11.19–14.25 to the right angle, 9.09–11.21 to the right lowest point, 11.87–14.92 to the left angle, and 9.92–12.76 to the left lowest point.The anatomic changes that occur in the aging face are delineated. With an adequate understanding of the anatomic changes that occur with aging, rhytidectomy can be approached as a reconstructive procedure, restoring facial soft tissue to its original state and location . In clinHowever in the present study, right versus left comparison in relation to inferior border of mandible was done Table . 33 Of 5Right MMN: Pearson correlation coefficient: 0.11. Linear regression of age: p = 0.46 (NS).Left MMN: Pearson correlation coefficient: 0.24. Linear regression of age: p = 0.15 (NS).Correlation and regression analysis of age to lowest position of MM nerve was done Fig. . The ANOSignificant difference in position with respect to age and left versus right comparisons was not found.Irrespective of the site of the skin incision, skin flaps should be carefully elevated in a plane immediately deep to the platysma and superficial to the investing layer of deep cervical fascia and marginal mandibular nerve. It is not the level of the skin incision that is important but the level of transection of the investing layer of cervical fascia. Knowledge of the dynamic and variable location of the marginal mandibular nerve relative to the inferior border of the mandible is useful in this regard. The decision to visualize the nerve needs to be individualized. If it is deemed necessary to divide the cervical fascia within 3–4 cm of the inferior border of the mandible it is the authors’ opinion that an attempt should be made to visualize the course of the nerve. The nerve is then preserved or sacrificed based on the oncologic objectives of the procedure. Electrical cautery should be used sparingly, and attention should be directed to avoiding traction or pressure injury from retractors .However, we recommend a novel surgical approach to the safe identification and preservation of the marginal mandibular nerve:Incision has to be placed 4 cm below inferior border of mandible. Elevation of sub-platysmal plane has to be performed till above the mandible, leaving behind the superficial fascia along with the facial lymphnodes. Meticulous dissection of superficial fascia has to be performed at mandible parallel to the course of the nerve to locate the MMN. Following the identification of MMN the facial lymph nodes (nodes of star) has to be dissected, sparing the MMN in case of malignancy, specially oral cavity cancer. This technique creates the field to dissect the nodes more aggressively simultaneously ensuring preservation of MMN, thus should be the preferable approach for oncological cases. Most of the patients in this study suffered from head and neck malignancy and none of them had any metastatic recurrence in the neck nodes. We advocate this technique for both malignant and non-malignant situations.There were some limitations:Quantitatively landmarking of the cervical branch. Also, the analysis of extent and etiology of disease, physical characteristics (neck circumference), and intra-operative positioning of patients.The in vivo course of the marginal mandibular nerve is significantly higher than previously published.The location of the nerve on the right does not correlate with the left.Location of the nerve does not correlate with patient’s age.


The Ser23 residue is shown to enhance ion transport via two mechanisms: creating a weak binding site, and increasing the effective hydrophilic length of the channel, both of which have previously been hypothesized in experiments. A two-dimensional free energy landscape has been computed to model multiple ion permeation, based on which a mechanism for ion conduction is proposed. It is shown that only one ion can pass through the channel at a time. This, along with a stretch of hydrophobic residues in the transmembrane domain of Vpu, explains the slow kinetics of ion conduction. The results are consistent with previous conductance studies that showed Vpu to be a weakly conducting ion channel.The viral protein U (Vpu) encoded by HIV-1 has been shown to assist in the detachment of virion particles from infected cells. Vpu forms cation-specific ion channels in host cells, and has been proposed as a potential drug target. An understanding of the mechanism of ion transport through Vpu is desirable, but remains limited because of the unavailability of an experimental structure of the channel. Using a structure of the pentameric form of Vpu – modeled and validated based on available experimental data – umbrella sampling molecular dynamics simulations (cumulative simulation time of more than 0.4 µs) were employed to elucidate the energetics and the molecular mechanism of ion transport in Vpu. Free energy profiles corresponding to the permeation of Na Xenopus oocytes, and in the plasma membrane of Escherichia coli+ and K+), and cannot differentiate between the two The viral protein U (Vpu) is one of the four accessory proteins encoded by HIV-1 that has an N-terminal transmembrane (TM) domain and a C-terminal cytoplasmic domain 1–81) and the Vpu TM region (Vpu1–32) excluding the cytoplasmic domain showed that the conductance states and ion-conduction recordings are similar for the two Channel recordings on full length Vpu (Vpu+ channel + rather than Na+ ions to pass through Molecular dynamics (MD) simulations have been successfully used to study transmembrane proteins in general The present study employs umbrella sampling MD simulations to elucidate the mechanism of ion conduction through the Vpu channel. We have recently reported a molecular model for the pentameric state of the TM domain of Vpu protein, which has been used here + ions and 18 Cl− ions, with a total of 31984 atoms. Prior to the current study, the system was equilibrated for 30 ns without any restraints and was found to be adequately equilibrated, as evidenced from the convergence of RMSD, the occurrence of several stabilizing intra-protein and protein-lipid interactions, and the retaining of the structural integrity of the channel, in general.The Vpu channel structure used in the study is a pentameric form of the TM region modeled in a recent study + and K+. For modeling the permeation of a K+ ion, the coordinates of a K+ ion from bulk water were first swapped with a water molecule at the C-terminus of the channel. Conformations with the K+ ion occurring at different positions along the axis of the pore were generated by pulling the ion along the pore axis using steered molecular dynamics (SMD) simulations. The ion was pulled at a constant velocity of 0.01 Å ps−1 by applying an external force on a dummy atom connected to the permeating ion via a spring with a harmonic constant of 10 kcal mol−1 Å−2. The structural model for the channel was aligned along the z-axis −1 Å−2 were applied on the heavy atoms of the protein to prevent the drifting of the helices during the pulling of the ion. Constant temperature and pressure were employed by using Langevin dynamics and a Langevin pressure piston, respectively. It must be noted that the SMD simulations were used to obtain the initial structures for the umbrella sampling simulations and not for investigating the permeation mechanism. The NAMD program +, the conformations were generated by replacing the K+ ion in the pore with an Na+ ion.The transport of two different ions through the channel was studied, namely Nai, the biasing potential has the formk is the harmonic constant, i,0z is the center of the window i, and z is the position of the ion along the reaction coordinate at any given instant. The potential energy function then has the formN denotes the positions of all the atoms in the system, and Eu(rN) is the unbiased potential energy function. The unbiased probability distribution of the ion along the pore axis iu(z)P is computed from the biased probability distribution ib(z)P, and is given byiF is a constant for window i. There are several approaches for determining iF, of which the most popular is the weighted histogram analysis method (WHAM) u(z)P using the relationi(z)p is the weight for window i which ensures that the statistical error for u(z)P is minimized. It is given byiN is the number of steps sampled for window i. iF is calculated using the relationu(z)P and iF are calculated in a self-consistent manner using the above equations.Umbrella sampling was performed by applying a biasing potential on the permeating ion, with the potential having a parabolic form. Independent simulations were performed for different positions of the ion along the pore axis, so that each simulation sampled the conformations of the system with the ion at the respective region. For a window z = −30 Å to z = 36 Å, giving a total of 133 windows along the z-axis spaced 0.5 Å apart . A distribution of ion positions around the center of a given window was obtained by applying a biasing potential with a force constant of 20 kcal mol−1 Å−2 on the ion using the MMFP module in the CHARMM program −1 mol−1 Å−2 were applied on the backbone Cα atoms of the protein to prevent the drifting of the channel. Ions other than the permeating ion were excluded from the pore region by using a repulsive sphere of radius 15 Å, with the repulsive force acting on ions only when they entered this sphere. Covalent bonds involving hydrogen were constrained using SHAKE Conformations with the ion placed at different places along the pore axis were extracted from the SMD simulation, and were used as initial structures for the different windows in the umbrella sampling calculations. The ion position ranged from + ions through the channel was modeled by considering different positions of one ion relative to the second ion, with the spacing between the two ions varying from 4 Å to 10 Å . A total of 395 windows spaced 1 Å apart were sampled with the two ions at different positions along the pore axis. A biasing harmonic potential of force constant 10 kcal mol−1 Å−2 was applied on the two ions. Parameters for the other restraints used were the same as those used for the calculations with a single ion in the pore. Equilibration and production runs for each window were carried out for 100 ps and 200 ps, respectively. The total simulation time combining all the single ion and two-ion simulations was more than 0.4 µs, with a total of 661 independent simulations. All molecular images were rendered using the visual molecular dynamics (VMD) program The permeation of two KA representation of the channel modeled in a hydrated lipid bilayer is shown in It is not practical to model events that occur at time scales longer than the ones that are practical with MD simulations. Additionally, insufficient sampling issues preclude calculation of free energies associated with such rare events. Use of umbrella sampling, which applies a harmonic potential along the predetermined reaction coordinate, allows sampling of intermediate states in the process of ion permeation with relatively less difficulty and with significantly less computing time, while at the same time allowing the calculation of the free energy change along the reaction coordinate using methods like WHAM + and K+ ions are shown in + and 43.3 kcal/mol for K+. Such a high energy barrier is to be expected, given the highly hydrophobic environment that prevails inside the channel. The energy barrier observed is considerably higher than that for other known ion channels The PMFs for the transport of Na+ and K+) were found to be very similar to each other. The movement of the ion into the channel from the C-terminal side is accompanied by the release of 2 kcal/mol of energy, with a shallow minimum occurring around z = −10 Å . These cutoff values were chosen accounting for the size of the respective ions z = 15 Å). This is explained by a slight widening of the pore around this region Solvation of the ion during the permeation process and its relationship with the free energy profiles were examined based on the hydration number, the number of water molecules in the first solvation shell of the ion and the interaction energies (see below). The permeating ion encounters two principal interacting partners inside the channel – the pore water molecules and the channel itself, and such interactions are expected to affect the free energy profiles significantly. Accordingly, interaction energies, which include the contributions of the electrostatic and Lennard-Jones (LJ) terms of the potential energy function, were calculated to examine the solvation energy. Mean values of the interaction energies between ion and water, and ion and protein are shown in + and K+ near the serine residue, suggesting weak binding ability. On the other hand, there is a remarkable enhancement of stability due to solvation as the ion moves towards the serine; this is seen as a fall in the solvation energy of the permeating ion. The serine residue therefore enhances ion movement into the channel by giving rise to a sufficiently solvated region on the C-terminal side. There are thus two ways in which the Ser23 makes conditions conducive for ion transport: firstly, it acts as a weak binding site, and, secondly, it gives rise to a hydrophilic region around the entrance of the pore.Previous biophysical studies have suggested that Ser23 might act as a weak binding site for ions + ions. The free energy landscape with respect to the position along the z-axis of the first ion and the distance of the second ion from the first is shown in To investigate if more than one ion can pass through the channel at a time, the free energy profile was calculated as a function of the positions of two permeating KIt may be noted that, although the windows for the two ion permeation were chosen such that the spacing between the two ions varied from 4 Å to 12 Å, the conformations sampled during the simulations cover a range of 3 Å to 14 Å. While conformations with the spacing close to 3 Å are sampled in the terminal regions of the channel, conformations with the spacing increasing to 14 Å are seen in the middle region of the channel. This suggests a propensity of the two ions to stay close together while they are near the hydrated terminal regions of the channel. On the other hand, in the middle region of the pore, the ions tend to stay as far apart as possible, thereby minimizing interionic repulsion.+ and Na+ through the Vpu channel can be attributed to the long stretch of hydrophobic residues which constrict the pore, and cause the dehydration of the pore lumen (α atoms of the protein (to prevent drifting) during the umbrella sampling simulations might hinder relaxation of the protein, and thereby cause the PMF to rise. However, it must be mentioned that the protein structure used here was previously subjected to unrestrained equilibration simulations in explicit solvent and bilayer for 30 ns, which is expected to be long enough for the protein backbone and sidechain atoms to relax. Furthermore, unlike transporters, ion channels do not usually undergo large scale domain motions during the process of solute transport, since they undergo gating prior to solute transport α atoms during the umbrella sampling is not likely to affect the dynamics in a significant way.The high energy barrier reported here for the transport of Kre lumen . It mighAn estimate of the rate of ion conduction can be made using the Arrhenius equation. An energy barrier of around 43 kcal/mol that is reported here suggests that the rate for the ion conduction to be several orders of magnitude lower than that estimated using the conductivity measurements previously reported by Mehnert et al. Another factor that could affect the quantification of properties of the channel is an inadequate representation (in simulations) of the conditions prevailing in electrophysiological experiments. Experimental channel recordings investigating selectivity in Vpu have been carried out under the application of a voltage + and K+ involves comparable energetic costs, explaining why the channel does not discriminate Na+ over K+. The results show that the Ser23 residue plays a role in ion channel activity by giving rise to a hydrophilic region in the pore, and by serving as a weak binding site. The possibility of multi-ion permeation has been investigated by computing the free energy as a function of the positions of two permeating ions. Results show that only one ion can pass at a time through the middle hydrophobic region of the channel. The mechanism proposed is able to account for the slow kinetics of ion transport across the channel, and it suggests a role for the hydrophobic stretch in controlling the kinetics of the process.Free energy profiles for conduction of monovalent cations across the Vpu channel have been characterized using umbrella sampling free energy calculations. The calculations reveal reasonably high energy barriers for ion movement through the channel, owing to the highly hydrophobic environment of the pore. The high energy barriers suggest that ion transport across the pore is kinetically slow, making Vpu a weakly conducting channel. The weak ion conducting activity is consistent with experimental biophysical studies, and has been explained based on the free energy calculations and hydration properties. The energy barriers arise from the desolvation of the ion as it moves from bulk water to the middle hydrophobic region of the channel. The permeation of NaFigure S1Orientation of important residues in the channel. (A) Glu28, Tyr29, Arg30, and Lys31 residues. Arg30 and Tyr29 are seen interacting with nearby lipid headgroups. Arg30 also forms a salt bridge with Glu28 on an adjacent helix. Lys31 faces the pore, but is very unlikely to exert any influence on the permeating ion, since it is shielded by a large number of water molecules. (B) Kink in the helix around the Ile17 residue.(TIF)Click here for additional data file.Figure S2Radial distribution function for water molecules around the permeating ion. (A) Na+ (B) K+.(TIF)Click here for additional data file.