3,648 research outputs found
Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields
The behavior of the nonlinear susceptibility and its relation to the
spin-glass transition temperature , in the presence of random fields, are
investigated. To accomplish this task, the Sherrington-Kirkpatrick model is
studied through the replica formalism, within a one-step
replica-symmetry-breaking procedure. In addition, the dependence of the
Almeida-Thouless eigenvalue (replicon) on the random fields
is analyzed. Particularly, in absence of random fields, the temperature
can be traced by a divergence in the spin-glass susceptibility ,
which presents a term inversely proportional to the replicon . As a result of a relation between and , the
latter also presents a divergence at , which comes as a direct consequence
of at . However, our results show that, in the
presence of random fields, presents a rounded maximum at a temperature
, which does not coincide with the spin-glass transition temperature
(i.e., for a given applied random field). Thus, the maximum
value of at reflects the effects of the random fields in the
paramagnetic phase, instead of the non-trivial ergodicity breaking associated
with the spin-glass phase transition. It is also shown that still
maintains a dependence on the replicon , although in a more
complicated way, as compared with the case without random fields. These results
are discussed in view of recent observations in the LiHoYF
compound.Comment: accepted for publication in PR
Jamming transition in a two-dimensional open granular pile with rolling resistance
We present a molecular dynamics study of the jamming/unjamming transition in
two-dimensional granular piles with open boundaries. The grains are modeled by
viscoelastic forces, Coulomb friction and resistance to rolling. Two models for
the rolling resistance interaction were assessed: one considers a constant
rolling friction coefficient, and the other one a strain dependent coefficient.
The piles are grown on a finite size substrate and subsequently discharged
through an orifice opened at the center of the substrate. Varying the orifice
width and taking the final height of the pile after the discharge as the order
parameter, one can devise a transition from a jammed regime (when the grain
flux is always clogged by an arch) to a catastrophic regime, in which the pile
is completely destroyed by an avalanche as large as the system size. A finite
size analysis shows that there is a finite orifice width associated with the
threshold for the unjamming transition, no matter the model used for the
microscopic interactions. As expected, the value of this threshold width
increases when rolling resistance is considered, and it depends on the model
used for the rolling friction.Comment: 9 pages, 6 figure
Busca e análise de notÃcias agrÃcolas sobre cana-de-açúcar.
Pretende-se fazer uma análise textual através do uso de mineração de texto, pelo método descrito por Moura et al. (2009), com o intuito de obter tópicos especÃficos, numa base de textos que consiste em notÃcias agrÃcolas sobre cana-de-açúcar. A base de textos é buscada por meio de um robô de busca em fontes previamente escolhidas (Jornal Cana: http://www.jornalcana.com.br). Após extração das notÃcias, é feito o tratamento dos textos e obtidas taxonomias de tópicos, isto é, são identificados assuntos e categorias cobertos pelo texto. Com os resultados da análise, pretende-se posteriormente localizar no espaço e no tempo os tópicos extraÃdos, para possibilitar uma inferência de fatores sócio-econômicos que possam influenciar na produção e safra da cana-de-açúcar
Quantum critical point in the spin glass-antiferromagnetism competition in Kondo-lattice systems
A theory is proposed to describe the competition among antiferromagnetism
(AF), spin glass (SG) and Kondo effect. The model describes two Kondo
sublattices with an intrasite Kondo interaction strength and an
interlattice quantum Ising interaction in the presence of a transverse field
. The interlattice coupling is a random Gaussian distributed variable
(with average and variance ) while the field is
introduced as a quantum mechanism to produce spin flipping. The path integral
formalism is used to study this fermionic problem where the spin operators are
represented by bilinear combinations of Grassmann fields. The disorder is
treated within the framework of the replica trick. The free energy and the
order parameters of the problem are obtained by using the static ansatz and by
choosing both and to allow, as previously,
a better comparison with the experimental findings.
The results indicate the presence of a SG solution at low and for
temperature ( is the freezing temperature). When is
increased, a mixed phase AF+SG appears, then an AF solution and finally a Kondo
state is obtained for high values of . Moreover, the behaviors of the
freezing and Neel temperatures are also affected by the relationship between
and the transverse field . The first one presents a slight
decrease while the second one decreases towards a Quantum Critical Point (QCP).
The obtained phase diagram has the same sequence as the experimental one for
, if is assumed to increase with , and
in addition, it also shows a qualitative agreement concerning the behavior of
the freezing and the Neel temperatures.Comment: 11 pages, 3 figures, accepted for publication in J. Phys.
Teaching Laminar-flow reactors: From experimentation to CFD simulation
An integrated chemical engineering lab experiment is described in this paper. It makes use of a laminar-flow tubular reactor (LFTR) through consecutive lab sessions. In a first session (not described here), the pseudo first-order kinetic constant for the reaction between crystal violet and sodium hydroxide is determined at different temperatures in a batch reactor. Then a tracer experiment is used to characterize the flow, pattern in the LFTR, and finally the steady-state conversion of crystal violet in the reactor is measured. For computing the theoretical reactor conversion, students must use the previously collected kinetic and tracer data, in a concept-integration exercise. A computational fluid dynamics (CFD) code (Fluent) is also used to simulate both the tracer and the isothermal reaction experiments performed in the LFTR. A very good agreement is obtained between experimental and simulated results and both only differ slightly from the theoretical predictions. The use of the CFD program is particularly noteworthy. For instance, transient simulations allow a very nice visualization of the tracer concentration front evolution, while the steady-state profiles along the axial position provide a good perspective of how reactant concentration varies within the reactor
Metastatic Testicular Germ Cell Tumor or a Chemoresponsive Liver Hemangioma?
Testicular germ cell tumors are the most common solid organ malignancy in young adult men. The presence of non-pulmonary visceral
metastasis is an independent factor that places such patients into the higher risk group. Hepatic hemangiomas are the most common
tumors of the liver and are entirely benign. Overlap between these entities may occur, particularly when metastases are hypervascular.
We describe a case of a 27-year-old man with a testicular germ cell tumor and a nodule in the right hepatic lobe suggestive of hemangioma.
After three cycles of chemotherapy, a size reduction in the hepatic nodule was confirmed, and this lesion was removed. Pathology revealed a
fibrosing hemangioma.
In this case report, the authors discuss the possible mechanisms for the hemangioma chemotherapy response
Non-Small Cell Lung Cancer: Screening, Diagnosis, and Staging
Lung cancer is the leading cause of cancer deaths worldwide. Tobacco consumption is the primary cause of lung cancer, accounting
for more than 85% 90% of all lung cancer deaths. Non-small cell lung cancer accounts for about 85% of all lung cancers.
Several studies have shown that low-dose helical CT of the lung detects more nodules and lung cancers, including early-stage cancers,
than does chest radiography. The National Lung Cancer Screening Trial results show that three annual rounds of low-dose CT screening
reduce mortality from lung cancer. Despite the great debate around lung cancer screening, recently the National Comprehensive Cancer
Network has come out in favor of lung cancer screening in an updated set of guidelines.
All patients who present with suspect lung cancer should have a complete and meticulous history and physical examination performed
to identify symptoms or physical findings suggestive of locally extensive or metastatic disease, assess pulmonary health status, identify
significant comorbidities, and assess overall health status.
Tissue sampling is required to confirm a diagnosis in all patients with suspected lung cancer. Non-surgical approaches, surgical
approaches, or both may be used to obtain a tissue sample. Evaluation of the mediastinal lymph nodes is a key step in the further staging
of the patient. The best way of evaluating mediastinal lymph nodes is still a matter of debate.
The tumor node metastasis (TNM) International Staging System provides useful prognostic information and is used to stage all patients
with non-small cell lung cancer.
Recent trials added new data on screening and diagnostic approach. Those data will be reviewed in this paper
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