507 research outputs found
Stroboscopic Laser Diagnostics for Detection of Ordering in One-Dimensional Ion beam
A novel diagnostic method for detecting ordering in one-dimensional ion beams
is presented. The ions are excited by a pulsed laser at two different positions
along the beam and fluorescence is observed by a group of four
photomultipliers. Correlation in fluorescence signals is firm indication that
the ion beam has an ordered structure.Comment: 7 pages, REVTEX, fig3 uuencoded, figs 1-2 available upon request from
[email protected], to appear in Phys. Rev.
Certification of Bounds of Non-linear Functions: the Templates Method
The aim of this work is to certify lower bounds for real-valued multivariate
functions, defined by semialgebraic or transcendental expressions. The
certificate must be, eventually, formally provable in a proof system such as
Coq. The application range for such a tool is widespread; for instance Hales'
proof of Kepler's conjecture yields thousands of inequalities. We introduce an
approximation algorithm, which combines ideas of the max-plus basis method (in
optimal control) and of the linear templates method developed by Manna et al.
(in static analysis). This algorithm consists in bounding some of the
constituents of the function by suprema of quadratic forms with a well chosen
curvature. This leads to semialgebraic optimization problems, solved by
sum-of-squares relaxations. Templates limit the blow up of these relaxations at
the price of coarsening the approximation. We illustrate the efficiency of our
framework with various examples from the literature and discuss the interfacing
with Coq.Comment: 16 pages, 3 figures, 2 table
Structural phase transitions in multipole traps
A small number of laser-cooled ions trapped in a linear radiofrequency
multipole trap forms a hollow tube structure. We have studied, by means of
molecular dynamics simulations, the structural transition from a double ring to
a single ring of ions. We show that the single-ring configuration has the
advantage to inhibit the thermal transfer from the rf-excited radial components
of the motion to the axial component, allowing to reach the Doppler limit
temperature along the direction of the trap axis. Once cooled in this
particular configuration, the ions experience an angular dependency of the
confinement if the local adiabaticity parameter exceeds the empirical limit.
Bunching of the ion structures can then be observed and an analytic expression
is proposed to take into account for this behaviour
Systemic leukotriene B<sub>4</sub> receptor antagonism lowers arterial blood pressure and improves autonomic function in the spontaneously hypertensive rat
KEY POINTS: Evidence indicates an association between hypertension and chronic systemic inflammation in both human hypertension and experimental animal models. Previous studies in the spontaneously hypertensive rat (SHR) support a role for leukotriene B(4) (LTB(4)), a potent chemoattractant involved in the inflammatory response, but its mode of action is poorly understood. In the SHR, we observed an increase in T cells and macrophages in the brainstem; in addition, gene expression profiling data showed that LTB(4) production, degradation and downstream signalling in the brainstem of the SHR are dynamically regulated during hypertension. When LTB(4) receptor 1 (BLT1) receptors were blocked with CPâ105,696, arterial pressure was reduced in the SHR compared to the normotensive control and this reduction was associated with a significant decrease in systolic blood pressure (BP) indicators. These data provide new evidence for the role of LTB(4) as an important neuroâimmune pathway in the development of hypertension and therefore may serve as a novel therapeutic target for the treatment of neurogenic hypertension. ABSTRACT: Accumulating evidence indicates an association between hypertension and chronic systemic inflammation in both human hypertension and experimental animal models. Previous studies in the spontaneously hypertensive rat (SHR) support a role for leukotriene B(4) (LTB(4)), a potent chemoattractant involved in the inflammatory response. However, the mechanism for LTB(4)âmediated inflammation in hypertension is poorly understood. Here we report in the SHR, increased brainstem infiltration of T cells and macrophages plus gene expression profiling data showing that LTB(4) production, degradation and downstream signalling in the brainstem of the SHR are dynamically regulated during hypertension. Chronic blockade of the LTB(4) receptor 1 (BLT1) receptor with CPâ105,696, reduced arterial pressure in the SHR compared to the normotensive control and this reduction was associated with a significant decrease in low and high frequency spectra of systolic blood pressure, and an increase in spontaneous baroreceptor reflex gain (sBRG). These data provide new evidence for the role of LTB(4) as an important neuroâimmune pathway in the development of hypertension and therefore may serve as a novel therapeutic target for the treatment of neurogenic hypertension
A Remarkable Three Hour Thermonuclear Burst From 4U 1820-30
We present a detailed observational and theoretical study of a ~3 hr long
X-ray burst (the ``super burst'') observed by the Rossi X-ray Timing Explorer
(RXTE) from the low mass X-ray binary (LMXB) 4U 1820-30. This is the longest
X-ray burst ever observed from this source, and perhaps one of the longest ever
observed in great detail from any source. We show that the super burst is
thermonuclear in origin. The level of the accretion driven flux as well as the
total energy release of ~1.5 x 10^{42} ergs indicate that helium could not be
the energy source for the super burst. We outline the physics relevant to
carbon production and burning on helium accreting neutron stars and present
calculations of the thermal evolution and stability of a carbon layer and show
that this process is the most likely explanation for the super burst. We show
that for large columns of accreted carbon fuel, a substantial fraction of the
energy released in the carbon burning layer is radiated away as neutrinos, and
the heat that is conducted from the burning layer in large part flows inward,
only to be released on timescales longer than the observed burst. Thus the
energy released possibly exceeds that observed in X-rays by more than a factor
of ten. Spectral analysis during the super burst reveals the presence of a
broad emission line between 5.8 - 6.4 keV and an edge at 8 - 9 keV likely due
to reflection of the burst flux from the inner accretion disk in 4U 1820-30. We
believe this is the first time such a signature has been unambiguously detected
in the spectrum of an X-ray burst.Comment: AASTEX, 44 pages, 14 figures. Accepted for publication in the
Astrophysical Journa
Promoter hypermethylation of the Chfr gene in neoplastic and non-neoplastic gastric epithelia
Nodal line resonance generating the giant anomalous Hall effect of CoSnS
Giant anomalous Hall effect (AHE) and magneto-optical activity can emerge in
magnets with topologically non-trivial degeneracies. However, identifying the
specific band structure features like Weyl points, nodal lines or planes which
generate the anomalous response is a challenging issue. Since the low-energy
interband transitions can govern the static AHE, we addressed this question in
the prototypical magnetic Weyl semimetal CoSnS also hosting nodal
lines by broadband polarized reflectivity and magneto-optical Kerr effect
spectroscopy with a focus on the far-infrared range. In the linear dichroism
spectrum we observe a strong resonance at 40\,meV, which also shows up in the
optical Hall conductivity spectrum and primarily determines the static AHE,
thus, confirms its intrinsic origin. Our material-specific theory reproduces
the experimental data remarkably well and shows that strongly tilted nodal line
segments around the Fermi energy generate the resonance. While the Weyl points
only give vanishing contributions, these segments of the nodal lines gapped by
the spin-orbit coupling dominate the low-energy optical response
Squeezing the periodicity of NĂ©el-type magnetic modulations by enhanced Dzyaloshinskii-Moriya interaction of 4d electrons
In polar magnets, such as GaVS, GaVSe and VOSeO, modulated magnetic phases namely the cycloidal and the NĂ©el-type skyrmion lattice states were identified over extended temperature ranges, even down to zero Kelvin. Our combined small-angle neutron scattering and magnetization study shows the robustness of the NĂ©el-type magnetic modulations also against magnetic fields up to 2âT in the polar GaMoS. In addition to the large upper critical field, enhanced spin-orbit coupling stabilize cycloidal, NĂ©el skyrmion lattice phases with sub-10ânm periodicity and a peculiar distribution of the magnetic modulation vectors. Moreover, we detected an additional single-q state not observed in any other polar magnets. Thus, our work demonstrates that non-centrosymmetric magnets with 4d and 5d electron systems may give rise to various highly compressed modulated states
Squeezing the periodicity of NĂ©el-type magnetic modulations by enhanced Dzyaloshinskii-Moriya interaction of 4d electrons
In polar magnets, such as GaVS, GaVSe and VOSeO, modulated magnetic phases namely the cycloidal and the NĂ©el-type skyrmion lattice states were identified over extended temperature ranges, even down to zero Kelvin. Our combined small-angle neutron scattering and magnetization study shows the robustness of the NĂ©el-type magnetic modulations also against magnetic fields up to 2âT in the polar GaMoS. In addition to the large upper critical field, enhanced spin-orbit coupling stabilize cycloidal, NĂ©el skyrmion lattice phases with sub-10ânm periodicity and a peculiar distribution of the magnetic modulation vectors. Moreover, we detected an additional single-q state not observed in any other polar magnets. Thus, our work demonstrates that non-centrosymmetric magnets with 4d and 5d electron systems may give rise to various highly compressed modulated states
Field dependence of the quantum ground state in the Shastry-Sutherland system SrCu(BO)
We present magnetic torque measurements on the Shastry-Sutherland quantum
spin system SrCu(BO) in fields up to 31 T and temperatures down to
50 mK. A new quantum phase is observed in a 1 T field range above the 1/8
plateau, in agreement with recent NMR results. Since the presence of the DM
coupling precludes the existence of a true Bose-Einstein condensation and the
formation of a supersolid phase in SrCu(BO), the exact nature of
the new phase in the vicinity of the plateau remains to be explained.
Comparison between magnetization and torque data reveals a huge contribution of
the Dzyaloshinskii-Moriya interaction to the torque response. Finally, our
measurements demonstrate the existence of a supercooling due to adiabatic
magnetocaloric effects in pulsed field experiments.Comment: submitted to European Physical Letter
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