1,048 research outputs found
Full Aging in Spin Glasses
The discovery of memory effects in the magnetization decays of spin glasses
in 1983 began a large effort to determine the exact nature of the decay. While
qualitative arguments have suggested that the decay functions should scale as
, the only time scale in the system, this type of scaling has not yet
been observed. In this letter we report strong evidence for the scaling of the
TRM magnetization decays as a function of . By varying the rate and the
profile that the sample is cooled through its transition temperature to the
measuring temperature, we find that the cooling plays a major role in
determining scaling. As the effective cooling time decreases, scaling improves and for we find almost perfect
scaling. We also find that subtraction of a stationary term
from the magnetization decay has a small effect on the scaling but changes the
form of the magnetization decay and improves overlap between curves produced
with different .Comment: 4 pages, 3 figure
Contemporary evaluation of the causes of cardiac tamponade: Acute and long-term outcomes
Background: Cardiac tamponade is a life-threatening state that complicates various medical conditions. The contemporary interventional era may have led to changes in clinical characteristics, causes and outcomes of cardiac tamponade.
Methods: We investigated all patients diagnosed with cardiac tamponade, based on clinical and echocardiographic findings, at a single medical center between the years 2000 and 2013. Data on medical history, index hospitalizations, pericardial fluid etiologies, and acute and long-term outcomes were collected.
Results: Cardiac tamponade was observed in 83 patients (52% females). Major etiologies included complications of percutaneous cardiac interventions (36%) and malignancies (primarily lung cancer; 23%), infectious/inflammatory causes (15%) and mechanical complications of myocardial infarction (12%). Sixteen (19%) patients died during the index hospitalization. Acute presentation of symptoms and lower quantity of effusion were associated with in-hospital mortality (p = 0.045 and p = 0.007). Tamponade secondary to malignancy was associated with the most substantial increment in post-discharge mortality (from 16% in-hospital to 68% 1-year mortality). During the mean follow-up of 45 months, 39 (45%) patients died. Malignancies, mechanical complications of myocardial infarction and bleeding/coagulation abnormalities were etiologies associated with poor survival (80% mortality during follow-up). Tamponade secondary to complications of percutaneous cardiac interventions or infectious/inflammatory causes were associated with significantly lower mortality (28% and 17%; log rank p < 0.001).
Conclusions: In a contemporary cohort, complications of percutaneous cardiac intervention replaced malignant diseases as the leading cause of cardiac tamponade. Nevertheless, these iatrogenic complications were associated with a relatively favorable outcome compared to tamponade induced by complications of myocardial infarction, coagulation abnormalities and malignant diseases.
Magnetocaloric Study of Spin Relaxation in `Frozen' Dipolar Spin Ice Dy2Ti2O7
The magnetocaloric effect of polycrystalline samples of pure and Y-doped
dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3 K
to 6 K and in magnetic fields of up to 2 T. As well as being of intrinsic
interest, it is proposed that the magnetocaloric effect may be used as an
appropriate tool for the qualitative study of slow relaxation processes in the
spin ice regime. In the high temperature regime the temperature change on
adiabatic demagnetization was found to be consistent with previously published
entropy versus temperature curves. At low temperatures (T < 0.4 K) cooling by
adiabatic demagnetization was followed by an irreversible rise in temperature
that persisted after the removal of the applied field. The relaxation time
derived from this temperature rise was found to increase rapidly down to 0.3 K.
The data near to 0.3 K indicated a transition into a metastable state with much
slower relaxation, supporting recent neutron scattering results. In addition,
magnetic dilution of 50 % concentration was found to significantly prolong the
dynamical response in the milikelvin temperature range, in contrast with
results reported for higher temperatures at which the spin correlations are
suppressed. These observations are discussed in terms of defects and loop
correlations in the spin ice state.Comment: 9 figures, submitted to Phys. Rev.
Phonon-phonon interactions and phonon damping in carbon nanotubes
We formulate and study the effective low-energy quantum theory of interacting
long-wavelength acoustic phonons in carbon nanotubes within the framework of
continuum elasticity theory. A general and analytical derivation of all three-
and four-phonon processes is provided, and the relevant coupling constants are
determined in terms of few elastic coefficients. Due to the low dimensionality
and the parabolic dispersion, the finite-temperature density of noninteracting
flexural phonons diverges, and a nonperturbative approach to their interactions
is necessary. Within a mean-field description, we find that a dynamical gap
opens. In practice, this gap is thermally smeared, but still has important
consequences. Using our theory, we compute the decay rates of acoustic phonons
due to phonon-phonon and electron-phonon interactions, implying upper bounds
for their quality factor.Comment: 15 pages, 2 figures, published versio
Coherent population trapping in ruby crystal at room temperature
Observation of coherent population trapping (CPT) at ground-state Zeeman
sublevels of -ion in ruby is reported. The experiments are performed
at room temperature by using both nanosecond optical pulses and nanosecond
trains of ultrashort pulses. In both cases sharp drops in the resonantly
induced fluorescence are detected as the external magnetic field is varied.
Theoretical analysis of CPT in a transient regime due to pulsed action of
optical pulses is presented.Comment: 4 pages, 4 figures, submitted to PR
Ultrafast demagnetization in the sp-d model: a theoretical study
We propose and analyze a theoretical model of ultrafast light-induced
magnetization dynamics in systems of localized spins that are coupled to
carriers' spins by sp-d exchange interaction. A prominent example of a class of
materials falling into this category are ferromagnetic (III,Mn)V
semiconductors, in which ultrafast demagnetization has been recently observed.
In the proposed model light excitation heats up the population of carriers,
taking it out of equilibrium with the localized spins. This triggers the
process of energy and angular momentum exchange between the two spin systems,
which lasts for the duration of the energy relaxation of the carriers. We
derive the Master equation for the density matrix of a localized spin
interacting with the hot carriers and couple it with a phenomenological
treatment of the carrier dynamics. We develop a general theory within the sp-d
model and we apply it to the ferromagnetic semiconductors, taking into account
the valence band structure of these materials. We show that the fast spin
relaxation of the carriers can sustain the flow of polarization between the
localized and itinerant spins leading to significant demagnetization of the
localized spin system, observed in (III,Mn)V materials.Comment: 15 pages, 8 figure
On the Nature of Memory and Rejuvenation in Glassy Systems
The memory effect in a single crystal spin glass
() has been measured using ac susceptibility techniques over a reduced temperature range of
and a model of the memory effect has been developed. A
double-waiting-time protocol is carried out where the spin glass is first
allowed to age at a temperature below , followed by a second aging at a
lower temperature after it has fully rejuvenated. The model is based on
calculating typical coincidences between the growth of correlated regions at
the two temperatures. It accounts for the absolute magnitude of the memory
effect as a function of both waiting times and temperatures. The data can be
explained by the memory loss being a function of the relative change in the
correlated volume at the first waiting temperature because of the growth in the
correlations at the second waiting temperature.Comment: 11 pages, 6 figure
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