16,936 research outputs found
Peltier ac calorimeter
A new ac calorimeter, utilizing the Peltier effect of a thermocouple junction
as an ac power source, is described. This Peltier ac calorimeter allows to
measure the absolute value of heat capacity of small solid samples with
sub-milligrams of mass. The calorimeter can also be used as a dynamic one with
a dynamic range of several decades at low frequencies.Comment: 12 pages, 4 figure
Relativistic Extension of a Charge-Conservative Finite Element Solver for Time-Dependent Maxwell-Vlasov Equations
In many problems involving particle accelerators and relativistic plasmas,
the accurate modeling of relativistic particle motion is essential for accurate
physical predictions. Here, we extend a charge-conserving finite element
time-domain (FETD) particle-in-cell (PIC) algorithm for the time-dependent
Maxwell-Vlasov equations on irregular (unstructured) meshes to the relativistic
regime by implementing and comparing three particle pushers: (relativistic)
Boris, Vay, and Higuera-Cary. We illustrate the application of the proposed
relativistic FETD-PIC algorithm for the analysis of particle cyclotron motion
at relativistic speeds, harmonic particle oscillation in the Lorentz-boosted
frame, and relativistic Bernstein modes in magnetized charge-neutral (pair)
plasmas.Comment: 25 pages, 9 figures, v3 with some minor corrections and title chang
Study of Solar Active Regions Based on BOAO Vector Magnetograms
In this study we present the study of solar active regions based on BOAO
vector magnetograms and filtergrams. With the new calibration method
we analyzed BOAO vector magnetograms taken from the SOFT observational system
to compare with those of other observing systems. In this study it has been
demonstrated that (1) our longitudinal magnetogram matches very well the
corresponding Mitaka's magnetogram to the extent that the maximum correlation
yields r=0.962 between our re-scaled longitudinal magnetogram and the Mitaka's
magnetogram; (2) according to a comparison of our magnetograms of AR 8422 with
those taken at Mitaka solar observatory their longitudinal fields are very
similar to each other while transverse fields are a little different possibly
due to large noise level; (3) main features seen by our longitudinal
magnetograms of AR 8422 and AR 8419 and the corresponding Kitt Peak
magnetograms are very similar to each other; (4) time series of our vector
magnetograms and H-alpha observations of AR 8419 during its flaring (M3.1/1B)
activity show that the filament eruption followed the sheared inversion line of
the quadrupolar configuration of sunspots, indicating that the flare should be
associated with the quadrupolar field configuration and its interaction with
new filament eruption. Finally, it may be concluded that the Solar Flare
Telescope at BOAO works normally and it is ready to do numerous observational
and theoretical works associated with solar activities such as flares.Comment: 8 pages, 8 figures, uses jkas99.sty, submitted to JKA
Evolution of Magnetic Non-potentiality associated with an X-class Flare in AR 6919
We present the evolution of magnetic nonpotentiality associated with an
X-class flare in AR 6919 using a set of MSO (Mees Solar Observatory)
magnetograms. The magnetogram data were obtained before and after the flare,
using the Haleakala Stokes Polarimeter which provides simultaneous Stokes
profiles of the Fe I doublet 6301.5 and 6302.5. A nonlinear least square method
was adopted to derive the magnetic field configuration from the observed Stokes
profiles and a multi-step ambiguity solution method was employed to resolve the
180 degree ambiguity. From the ambiguity-resolved vector magnetograms, we have
derived a set of physical quantities characterizing the field configuration
such as vertical current density, magnetic shear angle, angular shear and
magnetic free energy density. We have examined their changes before and after
the flare occurrence and obtained the following results. 1) There was a flux
decrease in both polarities around a delta-type sunspot region, where an
X-class flare occurred. 2) The vertical current near the delta sunspot region
was strongly enhanced before the flare. 3) The magnetic shear near the delta
sunspot region increased before the flare and then decreased after it. 4) The
sum of magnetic energy density significantly decreased before the flare onset,
implying that magnetic free energy was released through the flaring processes.Comment: 17 pages, 8 figures, uses kulwer.sty, submitted to Solar Physic
Evolution of Magnetic Field in AR 5747 and Its Approximation as a Linear Force Free Field
The evolution of nonpotential characteristics of magnetic fields in AR 5747
is presented using Mees Solar Observatory magnetograms taken on Oct. 20, 1989
to Oct. 22, 1989. The active region showed such violent flaring activities
during the observational span that strong X-ray flares took place including a
2B/X3 flare. The magnetogram data were obtained by the Haleakala Stokes
Polarimeter which provides simultaneous Stokes profiles of the Fe I doublet
6301.5 and 6302.5. A nonlinear least square method was adopted to derive the
magnetic field vectors from the observed Stokes profiles and a multi-step
ambiguity solution method was employed to resolve the 180 degree ambiguity.
From the ambiguity-resolved vector magnetograms, we have derived a set of
physical quantities characterizing the field configuration, which are magnetic
flux, vertical current density, magnetic shear angle, angular shear, magnetic
free energy density and a measure of magnetic field discontinuity MAD (Maximum
Angular Difference between two adjacent field vectors). In our results, all the
physical parameters decreased with time, which implies that the active region
was in a relaxation stage of its evolution. To examine the force-free
characteristics of the field, we calculated the integrated Lorentz force and
and also compared the longitudinal field component with the corresponding
vertical current density. In this investigation, we found that the magnetic
field in this active region was approximately linearly force-free throughout
the observing period. The time variation of the linear force-free coefficient
is consistent with the evolutionary trend of other nonpotentiality parameters.
This suggests that the linear force-free coefficient could be a good indicator
of the evolutionary status of active regions.Comment: 17 pages, 7 figures, uses kulwer.sty, submitted to Solar Physic
Strong magnetoelectric coupling in mixed ferrimagnetic-multiferroic phases of a double perovskite
Exploring new magnetic materials is essential for finding advantageous
functional properties such as magnetoresistance, magnetocaloric effect,
spintronic functionality, and multiferroicity. Versatile classes of double
perovskite compounds have been recently investigated because of intriguing
physical properties arising from the proper combination of several magnetic
ions. In this study, it is observed that the dominant ferrimagnetic phase is
coexisted with a minor multiferroic phase in single-crystalline
double-perovskite Er2CoMnO6. The majority portion of the ferrimagnetic order is
activated by the long-range order of Er3+ moments below TEr = 10 K in addition
to the ferromagnetic order of Co2+ and Mn4+ moments arising at TC = 67 K,
characterized by compensated magnetization at TComp = 3.15 K. The inverted
magnetic hysteresis loop observed below TComp can be described by an extended
Stoner-Wohlfarth model. The additional multiferroic phase is identified by the
ferroelectric polarization of 0.9 uC/m2 at 2 K. The coexisting ferrimagnetic
and multiferroic phases appear to be strongly correlated in that metamagnetic
and ferroelectric transitions occur simultaneously. The results based on
intricate magnetic correlations and phases in Er2CoMnO6 enrich fundamental and
applied research on magnetic materials through the scope of distinct magnetic
characteristics in double perovskites
High-stability, high-voltage power supplies for use with multi-reflection time-of-flight mass spectrographs
Achieving the highest possible mass resolving power in a multi-reflection
time-of-flight mass spectrometer requires very high-stability power supplies.
To this end, we have developed a programmable high-voltage power supply that
can achieve long-term stability on the order of parts-per-million. Herein we
present the design of the stable high-voltage system and bench-top stability
measurements up to 1~kV; the stabilization technique can, in principle, be
applied up to 15~kV or more.. We demonstrate that in the 1~Hz band the
output stability is on the level of 1~part per million (ppm) during one hour,
with only slightly more output variation across 3 days. We further demonstrate
that the output is largely free of noise in the 1~Hz -- 200~Hz band. We also
demonstrate settling to the ppm level within one minute following a 100~V step
transition. Finally, we demonstrate that when these power supplies are used to
bias the electrodes of a multi-reflection time-of-flight mass spectrograph the
measured time-of-flight is stable on the ppm-level for at least one hour.Comment: 10 pages, 12 figures, Report of electronics developmen
In-gas-cell laser spectroscopy for magnetic dipole moment of Pt toward 126
Magnetic dipole moment and mean-square charge radius of Pt
( 5/2) have been evaluated for the first time from the
investigation of the hyperfine splitting of the 248.792 nm
transition by in-gas-cell laser ionization spectroscopy. Neutron-rich nucleus
Pt was produced by multi-nucleon transfer reaction at the KISS where
the nuclear spectroscopy in the vicinity of 126 is planed from the aspect
of an astrophysical interest as well as the nuclear structure. Measured
magnetic dipole moment 0.63(13) is consistent with the
systematics of those of nuclei with 5/2. The deformation
parameter evaluated from the isotope shift indicates the
gradual shape change to spherical shape of platinum isotopes with increasing
neutron number toward 126.Comment: 8 pages, 5 figure
Thermodynamic evidence for nematic phase transition at the onset of pseudogap in YBaCuO
A central issue in the quest to understand the superconductivity in cuprates
is the nature and origin of the pseudogap state, which harbours anomalous
electronic states such as Fermi arc, charge density wave (CDW), and -wave
superconductivity. A fundamentally important, but long-standing controversial
problem has been whether the pseudogap state is a distinct thermodynamic phase
characterized by broken symmetries below the onset temperature .
Electronic nematicity, a fourfold () rotational symmetry breaking, has
emerged as a key feature inside the pseudogap regime, but the presence or
absence of a nematic phase transition and its relationship to the pseudogap
remain unresolved. Here we report thermodynamic measurements of magnetic torque
in the underdoped regime of orthorhombic YBaCuO with a field
rotating in the CuO plane, which allow us to quantify magnetic anisotropy
with exceptionally high precision. Upon entering the pseudogap regime, the
in-plane anisotropy of magnetic susceptibility increases after exhibiting a
distinct kink at . Our doping dependence analysis reveals that this
anisotropy is preserved below even in the limit where the effect of
orthorhombicity is eliminated. In addition, the excess in-plane anisotropy data
show a remarkable scaling behaviour with respect to in a wide doping
range. These results provide thermodynamic evidence that the pseudogap onset is
associated with a second-order nematic phase transition, which is distinct from
the CDW transition that accompanies translational symmetry breaking. This
suggests that nematic fluctuations near the pseudogap phase boundary have a
potential link to the strange metallic behaviour in the normal state, out of
which high- superconductivity emerges.Comment: 6 pages, 4 figures. An updated manuscript with SI will appear in
Nature Physic
Landau quantization in coupled Weyl points: a case study of semimetal NbP
Weyl semimetal (WSM) is a newly discovered quantum phase of matter that
exhibits topologically protected states characterized by two separated Weyl
points with linear dispersion in all directions. Here, via combining
theoretical analysis and magneto-infrared spectroscopy of an archetypal Weyl
semimetal, niobium phosphide, we demonstrate that the coupling between Weyl
points can significantly modify the electronic structure of a WSM and provide a
new twist to the protected states. These findings suggest that the coupled Weyl
points should be considered as the basis for analysis of realistic WSMs.Comment: Accepted in Nano Let
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