3,874 research outputs found
Subcentimeter Pulmonary Nodules Detected in Patients with Sarcoma
Background. Subcentimeter pulmonary nodules are being detected
with increasing frequency in patients with sarcoma due to the greater use of chest CT,
the advent of helical (spiral) CT scanning and multidetector scanners, and the attendant
decrease in image section thickness.Assessing the clinical significance of these pulmonary
nodules is of particular importance in sarcoma patients, due to the frequent occurrence of
pulmonary metastasis from sarcomas
Weakly correlated electrons on a square lattice: a renormalization group theory
We study the weakly interacting Hubbard model on the square lattice using a
one-loop renormalization group approach. The transition temperature T_c between
the metallic and (nearly) ordered states is found. In the parquet regime, (T_c
>> |mu|), the dominant correlations at temperatures below T_c are
antiferromagnetic while in the BCS regime (T_c << |mu|) at T_c the d-wave
singlet pairing susceptibility is most divergent.Comment: 12 pages, REVTEX, 3 figures included, submitted to Phys. Rev. Let
Layered XY-Models, Anyon Superconductors, and Spin-Liquids
The partition function of the double-layer model in the (dual) Villain
form is computed exactly in the limit of weak coupling between layers. Both
layers are found to be locked together through the
Berezinskii-Kosterlitz-Thouless transition, while they become decoupled well
inside the normal phase. These results are recovered in the general case of a
finite number of such layers. When re-interpreted in terms of the dual problems
of lattice anyon superconductivity and of spin-liquids, they also indicate that
the essential nature of the transition into the normal state found in two
dimensions persists in the case of a finite number of weakly coupled layers.Comment: 10 pgs, TeX, LA-UR-94-394
Updating DL-Lite ontologies through first-order queries
In this paper we study instance-level update in DL-LiteA, the description logic underlying the OWL 2 QL standard. In particular we focus on formula-based approaches to ABox insertion and deletion. We show that DL-LiteA, which is well-known for enjoying first-order rewritability of query answering, enjoys a first-order rewritability property also for updates. That is, every update can be reformulated into a set of insertion and deletion instructions computable through a nonrecursive datalog program. Such a program is readily translatable into a first-order query over the ABox considered as a database, and hence into SQL. By exploiting this result, we implement an update component for DLLiteA-based systems and perform some experiments showing that the approach works in practice.Peer ReviewedPostprint (author's final draft
Dynamic Exponent of t-J and t-J-W Model
Drude weight of optical conductivity is calculated at zero temperature by
exact diagonalization for the two-dimensional t-J model with the two-particle
term, . For the ordinary t-J model with =0, the scaling of the Drude
weight for small doping concentration is
obtained, which indicates anomalous dynamic exponent =4 of the Mott
transition. When is switched on, the dynamic exponent recovers its
conventional value =2. This corresponds to an incoherent-to-coherent
transition associated with the switching of the two-particle transfer.Comment: LaTeX, JPSJ-style, 4 pages, 5 eps files, to appear in J. Phys. Soc.
Jpn. vol.67, No.6 (1998
Adverse Moisture Events Predict Seasonal Abundance of Lyme Disease Vector Ticks (\u3cem\u3eIxodes scapularis\u3c/em\u3e)
Background
Lyme borreliosis (LB) is the most commonly reported vector-borne disease in north temperate regions worldwide, affecting an estimated 300,000 people annually in the United States alone. The incidence of LB is correlated with human exposure to its vector, the blacklegged tick (Ixodes scapularis). To date, attempts to model tick encounter risk based on environmental parameters have been equivocal. Previous studies have not considered (1) the differences between relative humidity (RH) in leaf litter and at weather stations, (2) the RH threshold that affects nymphal blacklegged tick survival, and (3) the time required below the threshold to induce mortality. We clarify the association between environmental moisture and tick survival by presenting a significant relationship between the total number of tick adverse moisture events (TAMEs - calculated as microclimatic periods below a RH threshold) and tick abundance each year.
Methods
We used a 14-year continuous statewide tick surveillance database and corresponding weather data from Rhode Island (RI), USA, to assess the effects of TAMEs on nymphal populations of I. scapularis. These TAMEs were defined as extended periods of time (\u3e8 h below 82% RH in leaf litter). We fit a sigmoid curve comparing weather station data to those collected by loggers placed in tick habitats to estimate RH experienced by nymphal ticks, and compiled the number of historical TAMEs during the 14-year record.
Results
The total number of TAMEs in June of each year was negatively related to total seasonal nymphal tick densities, suggesting that sub-threshold humidity episodes \u3e8 h in duration naturally lowered nymphal blacklegged tick abundance. Furthermore, TAMEs were positively related to the ratio of tick abundance early in the season when compared to late season, suggesting that lower than average tick abundance for a given year resulted from tick mortality and not from other factors.
Conclusions
Our results clarify the mechanism by which environmental moisture affects blacklegged tick populations, and offers the possibility to more accurately predict tick abundance and human LB incidence. We describe a method to forecast LB risk in endemic regions and identify the predictive role of microclimatic moisture conditions on tick encounter risk
A microscopic model for d-wave charge carrier pairing and non-Fermi-liquid behavior in a purely repulsive 2D electron system
We investigate a microscopic model for strongly correlated electrons with
both on-site and nearest neighbor Coulomb repulsion on a 2D square lattice.
This exhibits a state in which electrons undergo a ``somersault'' in their
internal spin-space (spin-flux) as they traverse a closed loop in external
coordinate space. When this spin-1/2 antiferromagnetic (AFM) insulator is
doped, the ground state is a liquid of charged, bosonic meron-vortices, which
for topological reasons are created in vortex-antivortex pairs. The magnetic
exchange energy of the distorted AFM background leads to a logarithmic
vortex-antivortex attraction which overcomes the direct Coulomb repulsion
between holes localized on the vortex cores. This leads to the appearance of
pre-formed charged pairs. We use the Configuration Interaction (CI) Method to
study the quantum translational and rotational motion of various charged
magnetic solitons and soliton pairs. The CI method systematically describes
fluctuation and quantum tunneling corrections to the Hartree-Fock Approximation
(HFA). We find that the lowest energy charged meron-antimeron pairs exhibit
d-wave rotational symmetry, consistent with the symmetry of the cuprate
superconducting order parameter. For a single hole in the 2D AFM plane, we find
a precursor to spin-charge separation in which a conventional charged
spin-polaron dissociates into a singly charged meron-antimeron pair. This model
provides a unified microscopic basis for (i) non-Fermi-liquid transport
properties, (ii) d-wave preformed charged carrier pairs, (iii) mid-infrared
optical absorption, (iv) destruction of AFM long range order with doping and
other magnetic properties, and (v) certain aspects of angled resolved
photo-emission spectroscopy (ARPES).Comment: 14 pages, 17 figure
C-axis Josephson Tunneling Between YBCO and Pb: Direct Evidence for Mixed Order Parameter Symmetry in a High-T_c Superconductor
We report a new class of -axis Josephson tunneling experiments in which a
conventional superconductor (Pb) is deposited across a single twin boundary of
a YBa_2Cu_3O_{7-\delta} crystal. We measure the critical current as a function
of magnitude and angle of magnetic field applied in the plane of the junction.
In all samples, we observe a clear experimental signature of an order parameter
phase shift across the twin boundary. These results provide strong evidence for
mixed - and -wave pairing in YBCO, with a reversal in the sign of the
-wave component across the twin boundary.Comment: 4 pages RevTex, 4 postscript figures included, submitted to Phys.
Rev. Let
- …