2,205 research outputs found
Spiral magnetic structure in spin-5/2 frustrated trimerized chains in SrMn3P4O14
We study a spin-5/2 antiferromagnetic trimerized chain substance SrMn3P4O14
using neutron powder diffraction experiments. The coplanar spiral magnetic
structure appears below T_N1 = 2.2(1) K. Values of several magnetic structure
parameters change rapidly at T_N2 = 1.75(5) K, indicating another phase
transition, although the magnetic structures above and below T_N2 are the
qualitatively same. The spiral magnetic structure can be explained by
frustration between nearest-neighbor and next-nearest-neighbor exchange
interactions in the trimerized chains.Comment: submitted to Phys. Rev.
Experimental measurement of the quantum geometric tensor using coupled qubits in diamond
Geometry and topology are fundamental concepts, which underlie a wide range
of fascinating physical phenomena such as topological states of matter and
topological defects. In quantum mechanics, the geometry of quantum states is
fully captured by the quantum geometric tensor. Using a qubit formed by an NV
center in diamond, we perform the first experimental measurement of the
complete quantum geometric tensor. Our approach builds on a strong connection
between coherent Rabi oscillations upon parametric modulations and the quantum
geometry of the underlying states. We then apply our method to a system of two
interacting qubits, by exploiting the coupling between the NV center spin and a
neighboring C nuclear spin. Our results establish coherent dynamical
responses as a versatile probe for quantum geometry, and they pave the way for
the detection of novel topological phenomena in solid state
Three-dimensional harmonic oscillator and time evolution in quantum mechanics
The problem of defining time (or phase) operator for three-dimensional
harmonic oscillator has been analyzed. A new formula for this operator has been
derived. The results have been used to demonstrate a possibility of
representing quantum-mechanical time evolution in the framework of an extended
Hilbert space structure. Physical interpretation of the extended structure has
been discussed shortly, too.Comment: 14 pages; submitted to Phys Rev
STUDY OF THE MECHANISM OF EXPLOSIVE FORCE PRODUCTION ON QUICK LIFT MOTION BY ANALYSIS OF EMG AND MOTION
The aim of this study is to investigate how explosive force exerts during power clean (PC) motion. The subjects are ten skilleds and ten unskilleds. The joint trajectory and EMG during PC are recorded. The joint torque and its rate of torque development (RTD) are calculated from the obtained data. The joint stiffness is estimated from joint stiffness index (JSI) calculated from EMG of agonist and antagonist muscle pair. Experimental results indicated that the skilleds showed the double knee bent that is typically seen in a stretch-shortening cycle (SSC). Skilleds exerted large values of RTD and JSI just after a period of exerting their small values during SSC. It indicates that a much amount of elastic energy stored in a low stiffness state is instantly transferred to the upper segments in the successive high stiffness state by “tenodesis action” of muscles. This is why large RTD generates in the skilled
Detecting bubbles in exotic nuclei
The occurrence of a bubble, due to an inversion of s state with the
state usually located above, is investigated. Proton bubbles in neutron-rich
Argon isotopes are optimal candidates. Pairing effects which can play against
the bubble formation are evaluated. They cannot prevent bubble formation in
very neutron-rich argon isotopes such as Ar. This pleads for a
measurement of the charge density of neutron-rich argon isotopes in the
forthcoming years, with the advent of electron scattering experiments in next
generation exotic beam facilities such as FAIR or RIBF.Comment: 6 pages, 5 figures, to be published in Nucl. Phys.
Relative property A and relative amenability for countable groups
We define a relative property A for a countable group with respect to a
finite family of subgroups. Many characterizations for relative property A are
given. In particular a relative bounded cohomological characterization shows
that if a group has property A relative to a family of subgroups, each of which
has property A, then the group has property A. This result leads to new classes
of groups that have property A. In particular, groups are of property A if they
act cocompactly on locally finite property A spaces of bounded geometry with at
least one stabilizer of property A. Specializing the definition of relative
property A, an analogue definition of relative amenability for discrete groups
are introduced and similar results are obtained.Comment: Updated to include a strengthening of the relative amenability
characterizatio
Exactness of locally compact groups
We give some new characterizations of exactness for locally compact second
countable groups. In particular, we prove that a locally compact second
countable group is exact if and only if it admits a topologically amenable
action on a compact Hausdorff space. This answers an open question by
Anantharaman-Delaroche.Comment: 18 pages, to appear in Adv. Mat
Co-firing of biomass with coals Part 1. Thermogravimetric kinetic analysis of combustion of fir (abies bornmulleriana) wood
The chemical composition and reactivity of fir (Abies bornmulleriana) wood under non-isothermal thermogravimetric (TG) conditions were studied. Oxidation of the wood sample at temperatures near 600 A degrees C caused the loss of aliphatics from the structure of the wood and created a char heavily containing C-O functionalities and of highly aromatic character. On-line FTIR recordings of the combustion of wood indicated the oxidation of carbonaceous and hydrogen content of the wood and release of some hydrocarbons due to pyrolysis reactions that occurred during combustion of the wood. TG analysis was used to study combustion of fir wood. Non-isothermal TG data were used to evaluate the kinetics of the combustion of this carbonaceous material. The article reports application of Ozawa-Flynn-Wall model to deal with non-isothermal TG data for the evaluation of the activation energy corresponding to the combustion of the fir wood. The average activation energy related to fir wood combustion was 128.9 kJ/mol, and the average reaction order for the combustion of wood was calculated as 0.30
- …