2,488 research outputs found
D1.2 Progress towards implementation of the fleet/fishery and indicator frameworks in the North Sea using Fcube
Sensing of Fluctuating Nanoscale Magnetic Fields Using NV Centres in Diamond
New magnetometry techniques based on Nitrogen-Vacancy (NV) defects in diamond
allow for the imaging of static (DC) and oscillatory (AC) nanoscopic magnetic
systems. However, these techniques require accurate knowledge and control of
the sample dynamics, and are thus limited in their ability to image fields
arising from rapidly fluctuating (FC) environments. We show here that FC fields
place restrictions on the DC field sensitivity of an NV qubit magnetometer, and
that by probing the dephasing rate of the qubit in a magnetic FC environment,
we are able to measure fluctuation rates and RMS field strengths that would be
otherwise inaccessible with the use of DC and AC magnetometry techniques. FC
sensitivities are shown to be comparable to those of AC fields, whilst
requiring no additional experimental overheads or control over the sample.Comment: 5 pages, 4 figure
Kinetic models of ion transport through a nanopore
Kinetic equations for the stationary state distribution function of ions
moving through narrow pores are solved for a number of one-dimensional models
of single ion transport. Ions move through pores of length , under the
action of a constant external field and of a concentration gradient. The
interaction of single ions with the confining pore surface and with water
molecules inside the pore are modelled by a Fokker-Planck term in the kinetic
equation, or by uncorrelated collisions with thermalizing centres distributed
along the pore. The temporary binding of ions to polar residues lining the pore
is modelled by stopping traps or energy barriers. Analytic expressions for the
stationary ion current through the pore are derived for several versions of the
model, as functions of key physical parameters. In all cases, saturation of the
current at high fields is predicted. Such simple models, for which results are
analytic, may prove useful in the study of the current/voltage relations of ion
channels through membranes
Optimization of the leak conductance in the squid giant axon
We report on a theoretical study showing that the leak conductance density,
\GL, in the squid giant axon appears to be optimal for the action potential
firing frequency. More precisely, the standard assumption that the leak current
is composed of chloride ions leads to the result that the experimental value
for \GL is very close to the optimal value in the Hodgkin-Huxley model which
minimizes the absolute refractory period of the action potential, thereby
maximizing the maximum firing frequency under stimulation by sharp, brief input
current spikes to one end of the axon. The measured value of \GL also appears
to be close to optimal for the frequency of repetitive firing caused by a
constant current input to one end of the axon, especially when temperature
variations are taken into account. If, by contrast, the leak current is assumed
to be composed of separate voltage-independent sodium and potassium currents,
then these optimizations are not observed.Comment: 9 pages; 9 figures; accepted for publication in Physical Review
Ultracoherence and Canonical Transformations
The (in)finite dimensional symplectic group of homogeneous canonical
transformations is represented on the bosonic Fock space by the action of the
group on the ultracoherent vectors, which are generalizations of the coherent
states.Comment: 24 page
Asymptotics of the colored Jones function of a knot
To a knot in 3-space, one can associate a sequence of Laurent polynomials,
whose th term is the th colored Jones polynomial. The paper is concerned
with the asymptotic behavior of the value of the th colored Jones polynomial
at e^{\a/n}, when \a is a fixed complex number and tends to infinity.
We analyze this asymptotic behavior to all orders in when \a is a
sufficiently small complex number. In addition, we give upper bounds for the
coefficients and degree of the th colored Jones polynomial, with
applications to upper bounds in the Generalized Volume Conjecture. Work of
Agol-Dunfield-Storm-W.Thurston implies that our bounds are asymptotically
optimal. Moreover, we give results for the Generalized Volume Conjecture when
\a is near . Our proofs use crucially the cyclotomic expansion of
the colored Jones function, due to Habiro.Comment: 31 pages, 13 figure
Ion-channel-like behavior in lipid bilayer membranes at the melting transition
It is well known that at the gel-liquid phase transition temperature a lipid
bilayer membrane exhibits an increased ion permeability. We analyze the
quantized currents in which the increased permeability presents itself. The
open time histogram shows a "-3/2" power law which implies an open-closed
transition rate that decreases like as time evolves. We
propose a "pore freezing" model to explain the observations. We discuss how
this model also leads to the noise that is commonly observed in
currents across biological and artificial membranes.Comment: 5 pages, 4 figure
Psi-series solutions of the cubic H\'{e}non-Heiles system and their convergence
The cubic H\'enon-Heiles system contains parameters, for most values of
which, the system is not integrable. In such parameter regimes, the general
solution is expressible in formal expansions about arbitrary movable branch
points, the so-called psi-series expansions. In this paper, the convergence of
known, as well as new, psi-series solutions on real time intervals is proved,
thereby establishing that the formal solutions are actual solutions
Oral medicine case book 68: Oral ulceration caused by rifampicin-resistant tuberculosis
A 53-year old female was referred by her local general
medical practitioner to an oral medicine specialist for the
management of a persistent ulcer on the left side of her tongue.
The lesion had been present for at least three months and
was not responding to treatment by topical antiseptic agents.
The earlier removal of a molar in close proximity to the lesion,
in an attempt to exclude the possibility of traumatic ulceration,
had also yielded no beneficial effects. Upon examination,
the patient appeared clinically healthy but presented with a
history of emphysema due to chronic cigarette smoking. The
emphysema was currently being managed by oral inhalation
steroids. Even though smoking cessation had previously been
advised, she failed to comply and was currently still smoking
more than 10 cigarettes per day.DHE
Fluctuations of a driven membrane in an electrolyte
We develop a model for a driven cell- or artificial membrane in an
electrolyte. The system is kept far from equilibrium by the application of a DC
electric field or by concentration gradients, which causes ions to flow through
specific ion-conducting units (representing pumps, channels or natural pores).
We consider the case of planar geometry and Debye-H\"{u}ckel regime, and obtain
the membrane equation of motion within Stokes hydrodynamics. At steady state,
the applied field causes an accumulation of charges close to the membrane,
which, similarly to the equilibrium case, can be described with renormalized
membrane tension and bending modulus. However, as opposed to the equilibrium
situation, we find new terms in the membrane equation of motion, which arise
specifically in the out-of-equilibrium case. We show that these terms lead in
certain conditions to instabilities.Comment: 7 pages, 2 figures. submitted to Europhys. Let
- …