79 research outputs found
The Adaptation Needs of International Social Work Students: A Proposed Mentoring Approach
Given the increasing numbers of international social work students in the United States, it is incumbent upon social work faculty to understand their needs for appropriate support as they adjust to life as foreign-born students. This paper has two main goals. First, we discuss contributions and challenges faced by international social work students. Second, as a form of support, we propose a mentoring approach pairing retired social work professionals with international social work students and argue that this may provide a mutually beneficial experience for both. That is, this study identifies adaptation needs specific to international social work students, describes the proposed paired-mentoring approach, and discusses implications of this approach
Stochastic resonance as a collective property of ion channel assemblies
By use of a stochastic generalization of the Hodgkin-Huxley model we
investigate both the phenomena of stochastic resonance (SR) and coherence
resonance (CR) in variable size patches of an excitable cell membrane. Our
focus is on the challenge how internal noise stemming from individual ion
channels does affect collective properties of the whole ensemble. We
investigate both an unperturbed situation with no applied stimuli and one in
which the membrane is stimulated externally by a periodic signal and additional
external noise. For the nondriven case, we demonstrate the existence of an
optimal size of the membrane patch for which the internal noise causes a most
regular spike activity. This phenomenon shall be termed intrinsic CR. In
presence of an applied periodic stimulus we demonstrate that the
signal-to-noise ratio (SNR) exhibits SR vs. decreasing patch size, or vs.
increasing internal noise strength, respectively. Moreover, we demonstrate that
conventional SR vs. the external noise intensity occurs only for sufficiently
large membrane patches, when the intensity of internal noise is below its
optimal level. Thus, biological SR seemingly is rooted in the collective
properties of large ion channel ensembles rather than in the individual
stochastic dynamics of single ion channels.Comment: 9 pages, 2 figure
Effective rate equations for the over-damped motion in fluctuating potentials
We discuss physical and mathematical aspects of the over-damped motion of a
Brownian particle in fluctuating potentials. It is shown that such a system can
be described quantitatively by fluctuating rates if the potential fluctuations
are slow compared to relaxation within the minima of the potential, and if the
position of the minima does not fluctuate. Effective rates can be calculated;
they describe the long-time dynamics of the system. Furthermore, we show the
existence of a stationary solution of the Fokker-Planck equation that describes
the motion within the fluctuating potential under some general conditions. We
also show that a stationary solution of the rate equations with fluctuating
rates exists.Comment: 18 pages, 2 figures, standard LaTeX2
Correlation studies of open and closed states fluctuations in an ion channel: Analysis of ion current through a large conductance locust potassium channel
Ion current fluctuations occurring within open and closed states of large
conductance locust potassium channel (BK channel) were investigated for the
existence of correlation. Both time series, extracted from the ion current
signal, were studied by the autocorrelation function (AFA) and the detrended
fluctuation analysis (DFA) methods. The persistent character of the short- and
middle-range correlations of time series is shown by the slow decay of the
autocorrelation function. The DFA exponent is significantly larger
than 0.5. The existence of strongly-persistent long-range correlations was
detected only for closed-states fluctuations, with . The
long-range correlation of the BK channel action is therefore determined by the
character of closed states. The main outcome of this study is that the memory
effect is present not only between successive conducting states of the channel
but also independently within the open and closed states themselves. As the ion
current fluctuations give information about the dynamics of the channel
protein, our results point to the correlated character of the protein movement
regardless whether the channel is in its open or closed state.Comment: 12 pages, 5 figures; to be published in Phys. Rev.
Stochastic Resonance in Ion Channels Characterized by Information Theory
We identify a unifying measure for stochastic resonance (SR) in voltage
dependent ion channels which comprises periodic (conventional), aperiodic and
nonstationary SR. Within a simplest setting, the gating dynamics is governed by
two-state conductance fluctuations, which switch at random time points between
two values. The corresponding continuous time point process is analyzed by
virtue of information theory. In pursuing this goal we evaluate for our
dynamics the tau-information, the mutual information and the rate of
information gain. As a main result we find an analytical formula for the rate
of information gain that solely involves the probability of the two channel
states and their noise averaged rates. For small voltage signals it simplifies
to a handy expression. Our findings are applied to study SR in a potassium
channel. We find that SR occurs only when the closed state is predominantly
dwelled. Upon increasing the probability for the open channel state the
application of an extra dose of noise monotonically deteriorates the rate of
information gain, i.e., no SR behavior occurs.Comment: 10 pages, 2 figures, to appear in Phys. Rev.
Femoral Stem Displacement in a Patient Suffering Recurrent Dislocations After Hip Hemiarthroplasty: Case Report
Displacement of the femoral component during attempt to closed reduction of a dislocated hip arthroplasty is an exceptionally rare, catastrophic event, which renders operative management obligatory. We report the proximal migration of a femoral stem during attempt to closed reduction in a patient with recurrent postoperative dislocations after hip hemiarthroplasty, and describe successful management by conversion to a standard total hip arthroplasty, retaining the same stem in the existing cement mantle. This illustrative case is reported not only as an extremely rare event, but also to highlight and discuss pitfalls and efficient measures in the management of this complex issue
Neutralization Tests of a mN FEEP Thruster
Neutralization of the ion beam produced by a FEEP thruster is in principle a task similar to the well-known problem of neutralizing a traditional ion rocket.On the other hand, the neutralization of a small, micronewton thrust level FEEP poses several practical problems. The neutralizer has to produce a very low electron current, that must couple with the very fast ions exhausted by the thruster. As the envisaged use of FEEP is based on its fine throttling capabilities, the neutralizer has to be proportionately able to follow the variations of the ion current, with the same rapidity. A first experimental assessment of the problem has been recently performed at Centrospazio. A series of test has been carried out on a 3 cm emitter, together with two neutralizers, namely a plasma bridge hollow cathode and a hot filament. The hollow cathode, developed by SEP, was fed by gaseous cæsium. A thoriated tungsten filament was also tested. The thruster and neutralizer operational parameters have been recorded, including the coupling potential between the neutralizer and the ion beam. In order to measure this potential, the thruster assembly was electrically isolated from the vacuum facility and kept floating during the tests. This paper presents the experimental setup and the test results. A critical analysis of the data gathered is provided, aimed at the identification of the optimal technology for a flight model
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