452 research outputs found

    Instability of sheared density interfaces

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    Examining paraphilia and emotional regulation with Norwegian speaking adults

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    Exploration of paraphilia has become an interesting topic for researchers the latest years. Norway lacks sufficient research on paraphilia. Current literature has shown distinct sex differences with men reporting more interest in paraphilia than women. Emotional regulation is suggested from research as a plausible psychological factor that could affect paraphilia. We started a collaboration with SIFER to explore paraphilia and emotional regulation from a non-clinical Norwegian-speaking sample. Two questionnaires were administered: The Paraphilia Scale and DERS-18. Data material was collected through an online study. 313 participants (N = 114 males, 191 females) took part in our study with age from 18 to over 50 years old. To simplify our analysis, The Paraphilia Scale was divided into 13 themes. Findings indicate evident sex differences when looking at paraphilic interests. Masochism and Sadism were the two most popular paraphilic themes for both male and female participants. The least popular themes were found to be Pedohebephilia and Zoophilia. The following paraphilic themes demonstrated sex differences: Biastophilia, Cro/Urophilia, Exhibitionism, Fetishism, Frotteurism, Pedohebephilia, Sadism, Somnophilia and Voyeurism. Male participants reported higher interest on these paraphilic themes. There were no sex differences when only assessing paraphilic behaviors. The relationship between paraphilic interests and paraphilic behaviors showed correlations that were moderate to strong on Biastophilia, Eroticized Gender, Masochism, Sadism, Telephone Scatologia and Voyeurism. The two questionnaires provide evidence showing only one significant association between emotional regulation and paraphilic interests. Implications of our results for research and clinical purposes on The Paraphilia Scale and DERS-18 are discussed

    Marginally unstable Holmboe modes

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    Marginally unstable Holmboe modes for smooth density and velocity profiles are studied. For a large family of flows and stratification that exhibit Holmboe instability, we show that the modes with phase velocity equal to the maximum or the minimum velocity of the shear are marginally unstable. This allows us to determine the critical value of the control parameter R (expressing the ratio of the velocity variation length scale to the density variation length scale) that Holmboe instability appears R=2. We then examine systems for which the parameter R is very close to this critical value. For this case we derive an analytical expression for the dispersion relation of the complex phase speed c(k) in the unstable region. The growth rate and the width of the region of unstable wave numbers has a very strong (exponential) dependence on the deviation of R from the critical value. Two specific examples are examined and the implications of the results are discussed.Comment: Submitted to Physics of Fluid

    Evolution of a barotropic shear layer into elliptical vortices

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    When a barotropic shear layer becomes unstable, it produces the well known Kelvin-Helmholtz instability (KH). The non-linear manifestation of KH is usually in the form of spiral billows. However, a piecewise linear shear layer produces a different type of KH characterized by elliptical vortices of constant vorticity connected via thin braids. Using direct numerical simulation and contour dynamics, we show that the interaction between two counter-propagating vorticity waves is solely responsible for this KH formation. We investigate the oscillation of the vorticity wave amplitude, the rotation and nutation of the elliptical vortex, and straining of the braids. Our analysis also provides possible explanation behind the formation and evolution of elliptical vortices appearing in geophysical and astrophysical flows, e.g. meddies, Stratospheric polar vortices, Jovian vortices, Neptune's Great Dark Spot and coherent vortices in the wind belts of Uranus.Comment: 7 pages, 4 figures, Accepted in Physical Review

    Stratified shear flow instabilities at large Richardson numbers

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    Numerical simulations of stratified shear flow instabilities are performed in two dimensions in the Boussinesq limit. The density variation length scale is chosen to be four times smaller than the velocity variation length scale so that Holmboe or Kelvin-Helmholtz unstable modes are present depending on the choice of the global Richardson number Ri. Three different values of Ri were examined Ri =0.2, 2, 20. The flows for the three examined values are all unstable due to different modes namely: the Kelvin-Helmholtz mode for Ri=0.2, the first Holmboe mode for Ri=2, and the second Holmboe mode for Ri=20 that has been discovered recently and it is the first time that it is examined in the non-linear stage. It is found that the amplitude of the velocity perturbation of the second Holmboe mode at the non-linear stage is smaller but comparable to first Holmboe mode. The increase of the potential energy however due to the second Holmboe modes is greater than that of the first mode. The Kelvin-Helmholtz mode is larger by two orders of magnitude in kinetic energy than the Holmboe modes and about ten times larger in potential energy than the Holmboe modes. The results in this paper suggest that although mixing is suppressed at large Richardson numbers it is not negligible, and turbulent mixing processes in strongly stratified environments can not be excluded.Comment: Submitted to Physics of Fluid

    Report on an experiment in five-day weather forecasting

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    The following report is presented as a statement of progress made at the Massachusetts Institute of Technology (M.I.T.) in the investigation into the possibility of extending the range of reliable weather forecasts. This project has been supported at M.I.T. and other private institutions by Bankhead-Jones appropriations since September, 1937. This report is concerned only with the work completed or in progress at M.I.T. The complementary program now in progress at the Weather Bureau in Washington is referred to only in so far as it has contributed directly to these investigations. Furthermore, the following report refers only to the last two years of the M.I.T. project. The first year of the three-year project was given over principally to the study of the results obtained by long range forecast methods already in use, and to the establishment of a northern hemisphere synoptic weather map procedure as a necessary precedent to the preparation of weekly forecasts on a synoptic basis. The results of the M.I.T. study of certain long range forecast methods already in practice are included in a general survey of such methods already published. The synoptic charts prepared at M.I.T. during that first year of the investigation are listed in an appendix to this report, together with those of the last two years. The preparation of weekly forecasts carried on during a part of that first year was so experimental in nature, and the procedure was so much changed the following year, that the results obtained were considered neither suffciently significant nor comparable enough with the later forecast results to merit any discussion. The present report is divided into three principal sections. Section I presents in condensed form our present conception of the essential nature of the general circulation, and discusses briefly the background of one or two of Professor Rossby's theoretical considerations concerning the general circulation which have found statistical and synoptic application in this investigation. Section II contains in brief form the results of synoptic and statistical checks of a large number of hypothetical relationships which might be assumed to hold in the earth's atmosphere. These include possible relationships in the large scale features of the general circulation, relationships between the general circulation and its different branches or centers of action, between the different branches or centers of action of the general circulation, between characteristics of the general circulation or its branches and anomalies of the meteorological elements in certain regions, between anomalies of the meteorological elements in one region and those in another region, and even between solar activity (sunspots) and characteristics of the general circulation or anomalies of the meteorological elements. The aim was to investigate possible interrelationships of all kinds, either with or without lag, in order to detect as many interaction principles or points as possible in the earth's atmosphere, whether they had direct or only the most indirect bearing on the forecast problem. The relationships investigated applied to daily, weekly, monthly, seasonal, or annual mean conditions. They were selected for investigation either from theoretical or practical considerations of the nature of the general circulation as outlined in Section I, or on the basis of popular beliefs which have long been current among meteorologists, or on the basis of direct observation of data which looked promising. The majority of these hypothetical relationships are found to be quite weak when subjected to rigid statistical checks, but all such results, whether positive or negative, are summarized in this report. Section III outlines the five-day forecast routine practice which has been carried on at M.I.T. during the greater part of the past two years on a weekly basis. It includes a statistical analysis of the verification results. In the conclusion are summarized the results of the investigation which thus far appear significant enough to justify their consideration in five-day or longer range forecasts. Suggestions are offered as to further steps which might profitably be taken if the investigation is to be continued. Finally there is an appendix in which are listed all the daily synoptic maps and mean charts and diagrams of surface and upper air data which have been plotted and analyzed at M.I.T. in connection with this project during the past three years. The importance of such a list is apparent when it is realized that inevitably in an investigation of this kind much the greater part of the time and effort expended is consumed in the routine or semiroutine duties involved in the preparation of such charts

    Relation between variations in the intensity of the zonal circulation of the atmosphere and the displacements of the permanent centers of action atmosphere and the displacements of the permanent centers of action

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    This paper attempts to interpret, from a single point of view, several at first sight independent phenomena brought into focus through the synoptic investigations carried on at the Massachusetts Institute of Technology during the last few years


    Interacting vorticity waves as an instability mechanism for magnetohydrodynamic shear instabilities

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    The interacting vorticity wave formalism for shear flow instabilities is extended here to the magnetohydrodynamic (MHD) setting, to provide a mechanistic description for the stabilising and destabilising of shear instabilities by the presence of a background magnetic field. The interpretation relies on local vorticity anomalies inducing a non-local velocity field, resulting in action-at-a-distance. It is shown here that the waves supported by the system are able to propagate vorticity via the Lorentz force, and waves may interact; existence of instability then rests upon whether the choice of basic state allows for phase-locking and constructive interference of the vorticity waves via mutual interaction. To substantiate this claim, we solve the instability problem of two representative basic states, one where a background magnetic field stabilises an unstable flow and the other where the field destabilises a stable flow, and perform relevant analyses to show how this mechanism operates in MHD.Comment: 25 pages, 11 figures, Journal of Fluid Mechanics template, submitted to Journal of Fluid Mechanics; comments welcome (v2: removed the redundant figure files in source zip file so resulting pdf really is 25 pages
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