1,527 research outputs found
Dynamic Radio-Frequency Transverse Susceptibility in Magnetic Nanoparticle Systems
A novel resonant method based on a tunnel-diode oscillator (TDO) is used to
study the dynamic transverse susceptibility in a Fe nanoparticle system. The
magnetic system consists of an aggregate of nanometer-size core (Au)-shell (Fe)
structure, synthesized by reverse micelle methods. Static and dynamic
magnetization measurements carried out in order to characterize the system
reveal a superparamagnetic behavior at high temperature. The field-dependent
transverse susceptibility at radio-frequencies (RF), for different temperatures
reveals distinct peak structure at characteristics fields (H_k, H_c) which
changes with temperature. It is proposed that relaxation processes could
explain the influence of the temperature on the field dependence of the
transverse susceptibility on the MI.Comment: 3 pages, 2-column, 3 figures, To be published in J. Appl. Phys. 2000
(44th Annual MMM proceedings
Integral Relaxation Time of Single-Domain Ferromagnetic Particles
The integral relaxation time \tau_{int} of thermoactivating noninteracting
single-domain ferromagnetic particles is calculated analytically in the
geometry with a magnetic field H applied parallel to the easy axis. It is shown
that the drastic deviation of \tau_{int}^{-1} from the lowest eigenvalue of the
Fokker-Planck equation \Lambda_1 at low temperatures, starting from some
critical value of H, is the consequence of the depletion of the upper potential
well. In these conditions the integral relaxation time consists of two
competing contributions corresponding to the overbarrier and intrawell
relaxation processes.Comment: 8 pages, 3 figure
XAX: a multi-ton, multi-target detection system for dark matter, double beta decay and pp solar neutrinos
A multi-target detection system XAX, comprising concentric 10 ton targets of
136Xe and 129/131Xe, together with a geometrically similar or larger target of
liquid Ar, is described. Each is configured as a two-phase
scintillation/ionization TPC detector, enhanced by a full 4pi array of
ultra-low radioactivity Quartz Photon Intensifying Detectors (QUPIDs) replacing
the conventional photomultipliers for detection of scintillation light. It is
shown that background levels in XAX can be reduced to the level required for
dark matter particle (WIMP) mass measurement at a 10^-10 pb WIMP-nucleon cross
section, with single-event sensitivity below 10^-11 pb. The use of multiple
target elements allows for confirmation of the A^2 dependence of a coherent
cross section, and the different Xe isotopes provide information on the
spin-dependence of the dark matter interaction. The event rates observed by Xe
and Ar would modulate annually with opposite phases from each other for WIMP
mass >~100 GeV/c^2. The large target mass of 136Xe and high degree of
background reduction allow neutrinoless double beta decay to be observed with
lifetimes of 10^27-10^28 years, corresponding to the Majorana neutrino mass
range 0.01-0.1 eV, the most likely range from observed neutrino mass
differences. The use of a 136Xe-depleted 129/131Xe target will also allow
measurement of the pp solar neutrino spectrum to a precision of 1-2%.Comment: 16 pages with 17 figure
Growth and magnetism of self-organized arrays of Fe(110) wires formed by deposition on kinetically grooved W(110)
Homoepitaxy of W(110) and Mo(110) is performed in a kinetically-limited
regime to yield a nanotemplate in the form of a uniaxial array of hills and
grooves aligned along the [001] direction. The topography and organization of
the grooves were studied with RHEED and STM. The nanofacets, of type {210}, are
tilted 18° away from (110). The lateral period could be varied from 4 to
12nm by tuning the deposition temperature. Magnetic nanowires were formed in
the grooves by deposition of Fe at 150°C on such templates. Fe/W wires
display an easy axis along [001] and a mean blocking temperature Tb=100KComment: Proceedings of ECOSS 2006 (Paris
Dynamics of allosteric transitions in GroEL
The chaperonin GroEL-GroES, a machine which helps some proteins to fold,
cycles through a number of allosteric states, the state, with high affinity
for substrate proteins (SPs), the ATP-bound state, and the
() complex. Structures are known for each
of these states. Here, we use a self-organized polymer (SOP) model for the
GroEL allosteric states and a general structure-based technique to simulate the
dynamics of allosteric transitions in two subunits of GroEL and the heptamer.
The transition, in which the apical domains undergo counter-clockwise
motion, is mediated by a multiple salt-bridge switch mechanism, in which a
series of salt-bridges break and form. The initial event in the transition, during which GroEL rotates clockwise, involves a
spectacular outside-in movement of helices K and L that results in K80-D359
salt-bridge formation. In both the transitions there is considerable
heterogeneity in the transition pathways. The transition state ensembles (TSEs)
connecting the , , and states are broad with the the
TSE for the transition being more plastic than the TSE. The results suggest that GroEL functions as a
force-transmitting device in which forces of about (5-30) pN may act on the SP
during the reaction cycle.Comment: 32 pages, 10 figures (Longer version than the one published
Increased Expression of Tissue Factor and Receptor for Advanced Glycation End Products in Peripheral Blood Mononuclear Cells of Patients With Type 2 Diabetes Mellitus with Vascular Complications
The aim of the study was to determine the correlation between
the expression of tissue factor (TF) and the receptor
for advanced glycation end products (RAGEs) and vascular
complications in patients with longstanding uncontrolled
type 2 diabetes (T2D). TF and RAGE mRNAs as well as
TF antigen and activity were investigated in 21 T2D patients
with and without vascular complications. mRNA expression
was assessed by reverse transcriptaseâpolymerase
chain reaction (RT-PCR) in nonstimulated and advanced
glycation end product (AGE) albuminâstimulated peripheral
blood mononuclear cells (PBMCs). TF antigen expression
was determined by enzyme-linked immunosorbent assay
(ELISA) and TF activity by a modified prothrombin
time assay. Basal RAGE mRNA expression was 0.2 ± 0.06
in patients with complications and 0.05 ± 0.06 patients without
complications (P = .004). Stimulation did not cause any
further increase in either group. TF mRNA was 0.58 ± 0.29
in patients with complications and 0.21 ± 0.18 in patients
without complications (P = .003). Stimulation resulted in
a nonsignificant increase in both groups. Basal TF activity
(U/106 PBMCs) was 18.4 ± 13.2 in patients with complications
and 6.96 ± 5.2 in patients without complications (P =
.003). It increased 3-fold in both groups after stimulation
(P = .001). TF antigen (pg/106 PBMCs) was 33.7 ± 28.6 in
patients with complications, 10.4 ± 7.8 in patients without complications (P = .02). Stimulation tripled TF antigen in
both groups of patients (P = .001). The RAGE/TF axis is
up-regulated inT2Dpatients with vascular complications as
compared to patients without complications. This suggests
a role for this axis in the pathogenesis of vascular complications
in T2D
A Spin-Mechanical Device for Detection and Control of Spin Current by Nanomechanical Torque
We propose a spin-mechanical device to control and detect spin currents by
mechanical torque. Our hybrid nano-electro-mechanical device, which contains a
nanowire with a ferromagnetic-nonmagnetic interface, is designed to measure or
induce spin polarized currents. Since spin carries angular momentum, a spin
flip or spin transfer process involves a change in angular momentum--and hence,
a torque--which enables mechanical measurement of spin flips. Conversely, an
applied torque can result in spin polarization and spin current.Comment: 6 pages, 2 figure
Evolution and stability of a magnetic vortex in small cylindrical ferromagnetic particle under applied field
The energy of a displaced magnetic vortex in a cylindrical particle made of
isotropic ferromagnetic material (magnetic dot) is calculated taking into
account the magnetic dipolar and the exchange interactions. Under the
simplifying assumption of small dot thickness the closed-form expressions for
the dot energy is written in a non-perturbative way as a function of the
coordinate of the vortex center. Then, the process of losing the stability of
the vortex under the influence of the externally applied magnetic field is
considered. The field destabilizing the vortex as well as the field when the
vortex energy is equal to the energy of a uniformly magnetized state are
calculated and presented as a function of dot geometry. The results (containing
no adjustable parameters) are compared to the recent experiment and are in good
agreement.Comment: 4 pages, 2 figures, RevTe
Nanostratification of optical excitation in self-interacting 1D arrays
The major assumption of the Lorentz-Lorenz theory about uniformity of local
fields and atomic polarization in dense material does not hold in finite groups
of atoms, as we reported earlier [A. E. Kaplan and S. N. Volkov, Phys. Rev.
Lett., v. 101, 133902 (2008)]. The uniformity is broken at sub-wavelength
scale, where the system may exhibit strong stratification of local field and
dipole polarization, with the strata period being much shorter than the
incident wavelength. In this paper, we further develop and advance that theory
for the most fundamental case of one-dimensional arrays, and study nanoscale
excitation of so called "locsitons" and their standing waves (strata) that
result in size-related resonances and related large field enhancement in finite
arrays of atoms. The locsitons may have a whole spectrum of spatial
frequencies, ranging from long waves, to an extent reminiscent of ferromagnetic
domains, -- to super-short waves, with neighboring atoms alternating their
polarizations, which are reminiscent of antiferromagnetic spin patterns. Of
great interest is the new kind of "hybrid" modes of excitation, greatly
departing from any magnetic analogies. We also study differences between
Ising-like near-neighbor approximation and the case where each atom interacts
with all other atoms in the array. We find an infinite number of "exponential
eigenmodes" in the lossless system in the latter case. At certain "magic"
numbers of atoms in the array, the system may exhibit self-induced (but linear
in the field) cancellation of resonant local-field suppression. We also studied
nonlinear modes of locsitons and found optical bistability and hysteresis in an
infinite array for the simplest modes.Comment: 39 pages, 5 figures; v2: Added the Conclusions section, corrected a
typo in Eq. (5.3), corrected minor stylistic and grammatical imperfection
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