501 research outputs found
^{63}Cu, ^{35}Cl, and ^{1}H NMR in the S=1/2 Kagom\'e Lattice ZnCu_{3}(OH)_{6}Cl_{2}
ZnCu(OH)Cl () is a promising new candidate for an
ideal Kagom\'e Heisenberg antiferromagnet, because there is no magnetic phase
transition down to 50 mK. We investigated its local magnetic and lattice
environments with NMR techniques. We demonstrate that the intrinsic local spin
susceptibility {\it decreases} toward T=0, but that slow freezing of the
lattice near 50 K, presumably associated with OH bonds, contributes to a
large increase of local spin susceptibility and its distribution. Spin dynamics
near T=0 obey a power-law behavior in high magnetic fields.Comment: Phys. Rev. Lett. (in press
Numerical methods for parameter identification in a convection-diffusion equation
We use a recently developed Sinc-Galerkin method for the solution of non-self-adjoint equations to solve a parameter identification problem arising from the one-dimensional convection-diffusion equation. This method is well suited for unbounded domains and certain singularities in the coefficients, as we illustrate by several examples. Practical aspects of implementation of this method are considered in detail
Magnetization Process of Kagome-Lattice Heisenberg Antiferromagnet
The magnetization process of the isotropic Heisenberg antiferromagnet on the
kagome lattice is studied. Data obtained from the numerical-diagonalization
method are reexamined from the viewpoint of the derivative of the magnetization
with respect to the magnetic field. We find that the behavior of the derivative
at approximately one-third of the height of the magnetization saturation is
markedly different from that for the cases of typical magnetization plateaux.
The magnetization process of the kagome-lattice antiferromagnet reveals a new
phenomenon, which we call the "magnetization ramp".Comment: 4 pages, 5figures, accepted in J. Phys. Soc. Jpn
Effect of compressive force on the performance of a proton exchange membrane fuel cell
The effect of the compressive force on the performance of a proton exchange membrane fuel cell has been examined experimentally. The performance has been evaluated on two polarization regions of the cell: ohmic and mass transport. Cell voltage and current density as a function of pressure were measured under constant load and various inlet air humidity conditions. The pressure distribution on the surface of the gas diffusion layer was measured using a pressure detection film and the results show that increasing the pressure improves the performance of the cell. The improvement of the cell voltage in the ohmic region was found to be greater than that in the mass transport region, whereas for the cell current density, the mass transport region exhibited higher change. The increase in the cell specific power in the ohmic and mass transport regions, as pressure increases from 0 to 2MNm-2, is estimated to be 9 and 18mWcm−2, respectively. However, the fuel cell performance in these two regions declined dramatically when excessive pressure (≥5 MNm−2) was applied. The mass transport region proved to be more susceptible to this sharp decline under excessive pressure than the ohmic region
The Herbertsmithite Hamiltonian: SR measurements on single crystals
We present transverse field muon spin rotation/relaxation measurements on
single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find
that the spins are more easily polarized when the field is perpendicular to the
kagome plane. We demonstrate that the difference in magnetization between the
different directions cannot be accounted for by Dzyaloshinksii-Moriya type
interactions alone, and that anisotropic axial interaction is present.Comment: 8 pages, 3 figures, accepted to JPCM special issue on geometrically
frustrated magnetis
Digital mobile technology facilitates HIPAA-sensitive perioperative messaging, improves physician-patient communication, and streamlines patient care
BackgroundMobile device technology has revolutionized interpersonal communication, but the application of this technology to the physician-patient relationship remains limited due to concerns over patient confidentiality and the security of digital information. Nevertheless, there is a continued focus on improving communication between doctors and patients in all fields of medicine as a means of improving patient care. In this study, we implement a novel communications platform to demonstrate that instantaneously sharing perioperative information with surgical patients and members of their support networks can improve patient care and strengthen the physician-patient relationship.Methods423 consecutive patients scheduled to undergo elective surgical procedures were offered complimentary registration to a secure, web-based service designed to distribute perioperative updates to a group of recipients designated by each patient via Short Message Service (SMS) and/or email. Messages were created by attending surgeons and delivered instantaneously through the web-based platform. In the postoperative period, patients and their designated message recipients, as well as participating healthcare providers, were asked to complete a survey designed to assess their experience with the messaging system. Survey results were statistically analyzed to determine satisfaction rates.ResultsOf the qualifying 423 patients, 313 opted to enroll in the study. On average, patients selected a total of 3.5 recipients to receive perioperative updates. A total of 1,195 electronic messages were generated for distribution to designated recipients during the study period and delivered to recipients located around the world. There were no documented errors or failures in message delivery. Satisfaction surveys were completed by 190 users of the service (73 %). Respondents identified themselves as either patients (n = 48, 25.5 %), family/friends (n = 120, 63.8 %), or healthcare providers (n = 15, 12 %). Satisfaction with the service was high: 94.2 % of users "enjoyed this software" and and 94.2 % of family/friends "felt more connected to their loved ones during surgery." 92.5 % would "recommend their loved ones sign up for this service". Ninety percent of patients who completed the survey reported "an improved hospital experience".ConclusionDigital communications platforms can facilitate the immediate transfer of HIPAA-compliant data to patients and their designees. Such systems can greatly improve the level of communication between physicians, patients, and patients' families and caregivers. All types of users, including healthcare professionals, patients, and their loved ones, recorded high levels of satisfaction. Based on these observations, we conclude that mobile digital communications platforms represent a way to harness the power of social media to enhance patient care
Slow Relaxation of Spin Structure in Exotic Ferromagnetic Phase of Ising-like Heisenberg Kagome Antiferromagnets
In the corner-sharing lattice, magnetic frustration causes macroscopic
degeneracy in the ground state, which prevents systems from ordering. However,
if the ensemble of the degenerate configuration has some global structure, the
system can have a symmetry breaking phenomenon and thus posses a finite
temperature phase transition. As a typical example of such cases, the magnetic
phase transition of the Ising-like Heisenberg antiferromagnetic model on the
kagome lattice has been studied. There, a phase transition of the
two-dimensional ferromagnetic Ising universality class occurs accompanying with
the uniform spontaneous magnetization. Because of the macroscopic degeneracy in
the ordered phase, the system is found to show an entropy-driven ordering
process, which is quantitatively characterized by the number of ``weathervane
loop''. We investigate this novel type of slow relaxation in regularly
frustrated system.Comment: 4 pages, 6 figure
Kondo physics in the algebraic spin liquid
We study Kondo physics in the algebraic spin liquid, recently proposed to
describe [Phys. Rev. Lett. {\bf 98}, 117205 (2007)].
Although spin dynamics of the algebraic spin liquid is described by massless
Dirac fermions, this problem differs from the Pseudogap Kondo model, because
the bulk physics in the algebraic spin liquid is governed by an interacting
fixed point where well-defined quasiparticle excitations are not allowed.
Considering an effective bulk model characterized by an anomalous critical
exponent, we derive an effective impurity action in the slave-boson context.
Performing the large- analysis with a spin index , we
find an impurity quantum phase transition from a decoupled local-moment state
to a Kondo-screened phase. We evaluate the impurity spin susceptibility and
specific heat coefficient at zero temperature, and find that such responses
follow power-law dependencies due to the anomalous exponent of the algebraic
spin liquid. Our main finding is that the Wilson's ratio for the magnetic
impurity depends strongly on the critical exponent in the zero temperature
limit. We propose that the Wilson's ratio for the magnetic impurity may be one
possible probe to reveal criticality of the bulk system
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