21,369 research outputs found
Anomalous physical properties of underdoped weak-ferromagnetic superconductor RuSrEuCuO
Similar to the optimal-doped, weak-ferromagnetic (WFM induced by canted
antiferromagnetism, T = 131 K) and superconducting (T = 56 K)
RuSrGdCuO, the underdoped RuSrEuCuO
(T = 133 K, T = 36 K) also exhibited a spontaneous vortex state
(SVS) between 16 K and 36 K. The low field (20 G) superconducting
hysteresis loop indicates a weak and narrow Meissner state region of average
lower critical field B(T) = B(0)[1 -
(T/T)], with B(0) = 7 G and T = 16 K. The
vortex melting transition (T = 21 K) below T obtained from
the broad resistivity drop and the onset of diamagnetic signal indicates a
vortex liquid region due to the coexistence and interplay between
superconductivity and WFM order. No visible jump in specific heat was observed
near T for Eu- and Gd-compound. This is not surprising, since the
electronic specific heat is easily overshadowed by the large phonon and
weak-ferromagnetic contributions. Furthermore, a broad resistivity transition
due to low vortex melting temperature would also lead to a correspondingly
reduced height of any specific heat jump. Finally, with the baseline from the
nonmagnetic Eu-compound, specific heat data analysis confirms the magnetic
entropy associated with antiferromagnetic ordering of Gd (J = S = 7/2)
at 2.5 K to be close to ln8 as expected.Comment: 7 figure
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A micro-electro-mechanical-system-based thermal shear-stress sensor with self-frequency compensation
By applying the micro-electro-mechanical-system (MEMS) fabrication technology, we developed a micro-thermal sensor to measure surface shear stress. The heat transfer from a polysilicon heater depends on the normal velocity gradient and thus provides the surface shear stress. However, the sensitivity of the shear-stress measurements in air is less than desirable due to the low heat capacity of air. A unique feature of this micro-sensor is that the heating element, a film 1 µm thick, is separated from the substrate by a vacuum cavity 2 µm thick. The vacuum cavity prevents the conduction of heat to the substrate and therefore improves the sensitivity by an order of magnitude. Owing to the low thermal inertia of the miniature sensing element, this shear-stress micro-sensor can provide instantaneous measurements of small-scale turbulence. Furthermore, MEMS technology allows us make multiple sensors on a single chip so that we can perform distributed measurements. In this study, we use multiple polysilicon sensor elements to improve the dynamic performance of the sensor itself. It is demonstrated that the frequency-response range of a constant-current sensor can be extended from the order of 100 Hz to 100 kHz
Micro Balloon Actuators for Aerodynamic Control
A robust, large-force, large-deflection micro balloon actuator for aerodynamic (manoeuvring) control of transonic aircraft has been developed. Using a novel process, high yield linear arrays of silicone balloons on a robust silicon substrate have been fabricated that can deflect vertically in excess of one mm. Balloon actuators have been tested under cyclic conditions to assess reliability. The actuators have been characterized in a wind tunnel to assess their suitability as aerodynamic control surfaces and flight-tested on a jet fighter to assess their resistance to varied temperatures and pressures at high velocity
Effect of solid-to-solvent ratio on phenolic content and antioxidant capacities of “ Dukung Anak” (Phyllanthus niruri)
The objective of this study was to evaluate the effects of solid-to-solvent ratio (1:5. 1:10, 1:15
and 1:20) on the extraction of phenolic compounds (TPC and TFC) and antioxidant capacity
(ABTS and DPPH radical scavenging capacity) of
P. niruri
. Solid-to-solvent ratio showed
a significant effect for both phenolic compounds (TPC and TFC) and antioxidant capacity
(ABTS and DPPH radical scavenging capacity) with 1:20 was the condition for extracting the
highest of phenolic compounds (TPC and TFC) with a value of 5788.7 mg GAE/100 g DW and
1906.5 mg CE/100 g DW, respectively and exhibited high antioxidant capacities (ABTS and
DPPH radical scavenging capacities) with a value of 0.820 mM and 1.598 mM, respectively
among the four levels studied. TPC was positively and significantly correlated with ABTS and
DPPH (r=0.999 and r=0.999) under the effects of solid-to-solvent ratio as compared to TFC,
positively and strongly correlated (r=0.865 and r=0.868) with ABTS and DPPH
Numerical Replica Limit for the Density Correlation of the Random Dirac Fermion
The zero mode wave function of a massless Dirac fermion in the presence of a
random gauge field is studied. The density correlation function is calculated
numerically and found to exhibit power law in the weak randomness with the
disorder dependent exponent. It deviates from the power law and the disorder
dependence becomes frozen in the strong randomness. A classical statistical
system is employed through the replica trick to interpret the results and the
direct evaluation of the replica limit is demonstrated numerically. The
analytic expression of the correlation function and the free energy are also
discussed with the replica symmetry breaking and the Liouville field theory.Comment: 5 pages, 4 figures, REVTe
Hubble Space Telescope H-Band Imaging Survey of Massive Gas-Rich Mergers
We report the results from a deep HST NICMOS H-band imaging survey of a
carefully selected sample of 33 luminous, late-stage galactic mergers at z <
0.3. Signs of a recent galactic interaction are seen in all of the objects in
the HST sample, including all 7 IR-excess Palomar-Green (PG) QSOs in the
sample. Unsuspected double nuclei are detected in 5 ULIRGs. A detailed
two-dimensional analysis of the surface brightness distributions in these
objects indicates that the great majority (81%) of the single-nucleus systems
show a prominent early-type morphology. However, low-surface-brightness
exponential disks are detected on large scale in at least 4 of these sources.
The hosts of 'warm' AGN-like systems are of early type and have less pronounced
merger-induced morphological anomalies than the hosts of cool systems with
LINER or HII region-like nuclear optical spectral types. The host sizes and
luminosities of the 7 PG~QSOs in our sample are statistically indistinguishable
from those of the ULIRG hosts. In comparison, highly luminous quasars, such as
those studied by Dunlop et al. (2003), have hosts which are larger and more
luminous. The hosts of ULIRGs and PG QSOs lie close to the locations of
intermediate-size (about 1 -- 2 L*) spheroids in the photometric projection of
the fundamental plane of ellipticals, although there is a tendency in our
sample for the ULIRGs with small hosts to be brighter than normal spheroids.
Excess emission from a young stellar population in the ULIRG/QSO hosts may be
at the origin of this difference. Our results provide support for a possible
merger-driven evolutionary connection between cool ULIRGs, warm ULIRGs, and
PG~QSOs although this sequence may break down at low luminosity. (abridged)Comment: Paper to be published in the Astrophysical Journal; revised based on
comments from referee. A PDF file combining both text and figures is
available at http://www.astro.umd.edu/~veilleux/pubs/nicmos.pd
Design of interpolative sigma-delta modulators via semi-indefinite programming
This correspondence considers the optimized design of interpolative sigma delta modulators (SDMs). The first optimization problem is to determine the denominator coefficients. The objective of the optimization problem is to minimize the passband energy of the denominator of the loop filter transfer function (excluding the dc poles) subject to the continuous constraint of this function defined in the frequency domain. The second optimization problem is to determine the numerator coefficients in which the cost function is to minimize the stopband ripple energy of the loop filter subject to the stability condition of the noise transfer function (NTF) and signal transfer function (STF). These two optimization problems are actually quadratic semi-infinite programming (SIP) problems. By employing the dual-parameterization method, global optimal solutions that satisfy the corresponding continuous constraints are guaranteed if the filter length is long enough. The advantages of this formulation are the guarantee of the stability of the transfer functions, applicability to design of rational infinite-impulse-response (IIR) filters without imposing specific filter structures, and the avoidance of iterative design of numerator and denominator coefficients. Our simulation results show that this design yields a significant improvement in the signal-to-noise ratio (SNR) and have a larger stability range, compared with the existing designs
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