158 research outputs found
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Microscopic Magnetic Stimulation of Neural Tissue
Electrical stimulation is currently used to treat a wide range of cardiovascular, sensory and neurological diseases. Despite its success, there are significant limitations to its application, including incompatibility with magnetic resonance imaging, limited control of electric fields and decreased performance associated with tissue inflammation. Magnetic stimulation overcomes these limitations but existing devices (that is, transcranial magnetic stimulation) are large, reducing their translation to chronic applications. In addition, existing devices are not effective for deeper, sub-cortical targets. Here we demonstrate that sub-millimeter coils can activate neuronal tissue. Interestingly, the results of both modelling and physiological experiments suggest that different spatial orientations of the coils relative to the neuronal tissue can be used to generate specific neural responses. These results raise the possibility that micro-magnetic stimulation coils, small enough to be implanted within the brain parenchyma, may prove to be an effective alternative to existing stimulation devices
Unambiguous state discrimination in quantum cryptography with weak coherent states
The use of linearly independent signal states in realistic implementations of
quantum key distribution (QKD) enables an eavesdropper to perform unambiguous
state discrimination. We explore quantitatively the limits for secure QKD
imposed by this fact taking into account that the receiver can monitor to some
extend the photon number statistics of the signals even with todays standard
detection schemes. We compare our attack to the beamsplitting attack and show
that security against beamsplitting attack does not necessarily imply security
against the attack considered here.Comment: 10 pages, 6 figures, updated version with added discussion of
beamsplitting attac
Dynamics of charged fluids and 1/L perturbation expansions
Some features of the calculation of fluid dynamo systems in
magnetohydrodynamics are studied. In the coupled set of the ordinary linear
differential equations for the spherically symmetric dynamos, the
problem represented by the presence of the mixed (Robin) boundary conditions is
addressed and a new treatment for it is proposed. The perturbation formalism of
large expansions is shown applicable and its main technical steps are
outlined.Comment: 16 p
Safety and efficacy of the immunosuppressive agent 6-tioguanine in murine model of acute and chronic colitis
<p>Abstract</p> <p>Background</p> <p>Oral thiopurines are effective and widely used in treatment of inflammatory bowel disease (IBD) in humans, although their use is limited due the development of adverse events. Here, we examine the efficacy and toxicity of oral treatment with 6-tioguanine (6-TG) and azathioprine (AZA) in a murine model of IBD.</p> <p>Methods</p> <p>We induced acute or chronic colitis in BALB/c mice by one or four cycles of 3% dextran sulphate sodium (DSS), respectively. Mice were treated by daily gavages of various dosages of 6-tioguanine, azathioprine, or by phosphate buffered saline (PBS) starting the first day of DSS or after two cycles of DSS, respectively. We monitored the efficacy and toxicity by measuring the weight change and serum alanine aminotransferase (ALT) activity and by disease severity and histology, at the end of the experiment. Moreover, we measured cytokine production after colon fragment cultivation by enzyme-linked immunoabsorbent assay and numbers of apoptotic cells in the spleen by flow cytometry.</p> <p>Results</p> <p>6-TG is effective in the treatment of acute DSS-induced colitis in a dose-dependent manner and 40 ÎŒg of 6-TG is significantly more effective in the treatment of acute colitis than both AZA and PBS. This effect is accompanied by decrease of IL-6 and IFN-Îł production in colon. We did not observe histological abnormalities in liver samples from control (PBS) or 6-TG treated mice. However, liver samples from most mice treated with AZA showed mild, yet distinct signs of hepatotoxicity. In chronic colitis, all thiopurine derivatives improved colitis, 20 ÎŒg of 6-TG per dose was superior. High doses of 6-TG led to significant weight loss at the end of the therapy, but none of the thiopurine derivatives increased levels of serum ALT. Both thiopurine derivatives reduced the proportion of apoptotic T helper cells, but a high production of both IL-6 and TGF-ÎČ was observed only in colon of AZA-treated mice.</p> <p>Conclusions</p> <p>Use of 6-TG in the treatment of experimental colitis in mice appears superior to AZA administration and placebo. In contrast to 6-TG, the use of AZA resulted in histological liver abnormalities.</p
Non linear pseudo-bosons versus hidden Hermiticity. II: The case of unbounded operators
Parallels between the notions of nonlinear pseudobosons and of an apparent
non-Hermiticity of observables as shown in paper I (arXiv: 1109.0605) are
demonstrated to survive the transition to the quantum models based on the use
of unbounded metric in the Hilbert space of states.Comment: 21 p
Solvability and PT-symmetry in a double-well model with point interactions
We show that and how point interactions offer one of the most suitable guides
towards a quantitative analysis of properties of certain specific non-Hermitian
(usually called PT-symmetric) quantum-mechanical systems. A double-well model
is chosen, an easy solvability of which clarifies the mechanisms of the
unavoided level crossing and of the spontaneous PT-symmetry breaking. The
latter phenomenon takes place at a certain natural boundary of the domain of
the "acceptable" parameters of the model. Within this domain the model mediates
a nice and compact explicit illustration of the not entirely standard
probabilistic interpretation of the physical bound states in the very recently
developed (so called PT symmetric or, in an alternative terminology,
pseudo-Hermitian) new, fairly exciting and very quickly developing branch of
Quantum Mechanics.Comment: 24 p., written for the special journal issue "Singular Interactions
in Quantum Mechanics: Solvable Models". Will be also presented to the int.
conference "Pseudo-Hermitian Hamiltonians in Quantum Physics III" (Instanbul,
Koc University, June 20 - 22, 2005)
http://home.ku.edu.tr/~amostafazadeh/workshop/workshop.ht
PT-symmetric regularizations in supersymmetric quantum mechanics
Supersymmetry offers one of the deepest insights in the concept of
solvability in quantum mechanics. This insight is, paradoxically, restricted by
one of the most serious formal drawbacks of the standard Witten's formulation
of supersymmetric quantum mechanics which lies in the Jevicki-Rodrigues'
postulate of absence of poles in superpotentials W(x) over all the real axis of
coordinates x. In our review we emphasize that this obstacle is artificial and
that it disappears immediately after a suitable (say, constant) shift of the
axis of x into complex plane. Detailed attention is paid to a close
relationship between this common trick and the recent not quite expected
increase of interest in non-Hermitian (a. k. a. PT-symmetric or
pseudo-Hermitian) Hamiltonians. We show that the resulting PT-SUSY
regularization recipe proves both easy and universal. An insight into its
mathematics is mediated by the complex harmonic oscillator with a
centrifugal-like spike. An exhaustive discussion of the role of the strength of
this spike is offered. In addition we recollect the possibility of a
re-formulation of the recipe in the second-order SUSY language. Finally we list
a few promising directions of applicability of our PT-SUSY regularization
prescription to a few more complicated nonrelativistic models (superintegrable
Hamiltonians of the Smorodinsky-Winternitz and of the Calogero-Sutherland type)
and to the relativistic Klein-Gordon equation (as well as to all of its
unphysical higher-order analogues).Comment: 17 pages, based on the talk during SUSY QM conference in Valladolid
in the summer in 2003, to appear in J. Phys. A: Math. Gen. (spec. issue
The Security of Practical Quantum Key Distribution
Quantum key distribution (QKD) is the first quantum information task to reach
the level of mature technology, already fit for commercialization. It aims at
the creation of a secret key between authorized partners connected by a quantum
channel and a classical authenticated channel. The security of the key can in
principle be guaranteed without putting any restriction on the eavesdropper's
power.
The first two sections provide a concise up-to-date review of QKD, biased
toward the practical side. The rest of the paper presents the essential
theoretical tools that have been developed to assess the security of the main
experimental platforms (discrete variables, continuous variables and
distributed-phase-reference protocols).Comment: Identical to the published version, up to cosmetic editorial change
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Molecular MR Imaging of Liver Fibrosis: A Feasibility Study Using Rat and Mouse Models
Background & Aims: Liver biopsy, the current clinical gold standard for fibrosis assessment, is invasive and has sampling errors, and is not optimal for screening, monitoring, or clinical decision-making. Fibrosis is characterized by excessive accumulation of extracellular matrix proteins including type I collagen. We hypothesize that molecular magnetic resonance imaging (MRI) with a probe targeted to type I collagen could provide a direct and non-invasive method of fibrosis assessment. Methods: Liver fibrosis was induced in rats with diethylnitrosamine and in mice with carbon tetrachloride. Animals were imaged prior to and immediately following i.v. administration of either collagen-targeted probe EP-3533 or non-targeted control Gd-DTPA. Magnetic resonance (MR) signal washout characteristics were evaluated from T1 maps and T1-weighted images. Liver tissue was subjected to pathologic scoring of fibrosis and analyzed for gadolinium and hydroxyproline. Results: EP-3533-enhanced MR showed greater signal intensity on delayed imaging (normalized signal enhancement mice: controlâ
=â
0.39â
屉
0.04, fibroticâ
=â
0.55â
屉
0.03, pâ
<0.01) and slower signal washout in the fibrotic liver compared to controls (liver t1/2â
=â
51.3â
屉
3.6 vs. 42.0â
屉
2.5â
min, pâ
<0.05 and 54.5â
屉
1.9 vs. 44.1â
屉
2.9â
min, pâ
<0.01 for fibrotic vs. controls in rat and mouse models, respectively). Gd-DTPA-enhanced MR could not distinguish fibrotic from control animals. EP-3533 gadolinium concentration in the liver showed strong positive correlations with hydroxyproline levels (râ
=â
0.74 (rats), râ
=â
0.77 (mice)) and with Ishak scoring (râ
=â
0.84 (rats), râ
=â
0.79 (mice)). Conclusions: Molecular MRI of liver fibrosis with a collagen-specific probe identifies fibrotic tissue in two rodent models of disease
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