2,499 research outputs found
Investigation of the reaction of the lunar surface to the impact of a lunar probe final report
Flash phenomena associated with hypervelocity impact for estimating flash from impact of lunar prob
Coexistence and competition of local- and long-range polar orders in a ferroelectric relaxor
We have performed a series of neutron diffuse scattering measurements on a
single crystal of the solid solution Pb(ZnNb)O (PZN) doped
with 8% PbTiO (PT), a relaxor compound with a Curie temperature T K, in an effort to study the change in local polar orders from the polar
nanoregions (PNR) when the material enters the ferroelectric phase. The diffuse
scattering intensity increases monotonically upon cooling in zero field, while
the rate of increase varies dramatically around different Bragg peaks. These
results can be explained by assuming that corresponding changes occur in the
ratio of the optic and acoustic components of the atomic displacements within
the PNR. Cooling in the presence of a modest electric field oriented
along the [111] direction alters the shape of diffuse scattering in reciprocal
space, but does not eliminate the scattering as would be expected in the case
of a classic ferroelectric material. This suggests that a field-induced
redistribution of the PNR has taken place
Density matrix renormalisation group for a quantum spin chain at non-zero temperature
We apply a recent adaptation of White's density matrix renormalisation group
(DMRG) method to a simple quantum spin model, the dimerised chain, in
order to assess the applicabilty of the DMRG to quantum systems at non-zero
temperature. We find that very reasonable results can be obtained for the
thermodynamic functions down to low temperatures using a very small basis set.
Low temperature results are found to be most accurate in the case when there is
a substantial energy gap.Comment: 6 pages, Standard Latex File + 7 PostScript figures available on
reques
The Persistence and Memory of Polar Nano-Regions in a Ferroelectric Relaxor Under an Electric Field
The response of polar nanoregions (PNR) in the relaxor compound
Pb[(ZnNb)Ti]O subject to a [111]-oriented
electric field has been studied by neutron diffuse scattering. Contrary to
classical expectations, the diffuse scattering associated with the PNR
persists, and is even partially enhanced by field cooling. The effect of the
external electric field is retained by the PNR after the field is removed. The
``memory'' of the applied field reappears even after heating the system above
, and cooling in zero field
Anomalous transverse acoustic phonon broadening in the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O_3
The intrinsic linewidth of the transverse acoustic (TA) phonon
observed in the relaxor ferroelectric compound
Pb(MgNbTiO (PMN-20%PT) begins to broaden
with decreasing temperature around 650 K, nearly 300 K above the ferroelectric
transition temperature ( K). We speculate that this anomalous
behavior is directly related to the condensation of polarized, nanometer-sized,
regions at the Burns temperature . We also observe the ``waterfall''
anomaly previously seen in pure PMN, in which the transverse optic (TO) branch
appears to drop precipitously into the TA branch at a finite momentum transfer
\AA. The waterfall feature is seen even at
temperatures above . This latter result suggests that the PNR exist as
dynamic entities above .Comment: 6 pages, 4 figure
Fully automatic meningioma segmentation using T1-weighted contrast-enhanced MR images only
Background Manual segmentation of brain tumors requires expertise, is time-consuming, and is subject to inter-rater variability. Fully automatic brain tumor segmentation is possible for glioma and meningioma when volumetric T1, T1 contrast-enhanced (T1c), T2, and Fluid-attenuated inversion recovery (FLAIR) MRIs are available. In clinical care of meningiomas, however, often only volumetric T1c scans are available. In this work, we trained a deep learning network to segment meningiomas using only T1c scans for use in clinical research. Material and Methods NnU-Net, a deep learning model that is optimized for medical image segmentation, was trained to segment meningiomas from T1c images. This was performed on a large clinically collected meningioma dataset (n=374) of T1c scans with semi-automatically generated enhancing tumor masks and additional data from the BraTS2020 glioma dataset. Model performance was compared against inter-rater reliability, between different models, between anatomical tumor locations, and against models using multiple MRI modalities. Results The best performing model obtained a Dice score of 0.90. This performance was 0.03 points lower when compared to inter-rater reliability (Dice=0.93) and almost equal to models using multiple MRI modalities. Model performance split over anatomical tumor locations was between 0.90 and 0.97 (Dice). Conclusion Fully automatic meningioma segmentation using only T1c images is possible with an accuracy that is similar to inter-rater reliability and models using multiple imaging modalities
A study to examine the relationship between uterine pathology and depletion of oxytetracycline in plasma and milk after intrauterine infusion
Citation: Gorden, P. J., Ydstie, J., Kleinhenz, M. D., Wulf, L. W., Gehring, R., Wang, C., & Coetzee, J. F. (2016). A study to examine the relationship between uterine pathology and depletion of oxytetracycline in plasma and milk after intrauterine infusion. Journal of Animal Science, 94, 30-30. doi:10.2527/msasas2016-065Metritis is a frequent problem in postpartum dairy cows. Intrauterine therapy with oxytetracycline (OTC) is often used to improve therapeutic outcomes, although efficacy data supporting this therapy are ambiguous. Several manuscripts describe the depletion of OTC from milk following intrauterine therapy. However, none of these studies have correlated uterine severity scores with milk OTC concentrations using highly sensitive detection systems. Our objective was to do this to test the hypothesis that cows with more severe uterine severity would have higher OTC residues in milk following intrauterine therapy. Thirty-two cows received a single treatment of 4 g of OTC via intrauterine infusion. Blood and milk samples were collected before intrauterine therapy and throughout the trial period of 96 h after infusion. Uterine severity scores were assigned at initiation of therapy and every 24 h throughout the remainder of the trial. Plasma and milk samples were analyzed for OTC concentrations using liquid chromatography coupled with mass spectrometry. Following treatment, OTC rapidly diffused from the uterus to plasma and from plasma to milk. Maximum concentration in plasma and milk occurred within 24 h following intrauterine infusion and 18 of the cows still had detectable levels of OTC in milk 4 d after intrauterine infusion. Greater uterine severity score at the initiation of treatment showed a significant positively correlation with higher milk OTC concentration at the second milking following treatment (R2 = 0.46, P = 0.01) but there was no correlation between initial uterine severity score and OTC concentration at the conclusion of the study (R2 = ?0.06, P = 0.75). In the United States, intrauterine administration of OTC is considered to be an extra-label therapy. The use of uterine severity score can be used to predict OTC concentration in the first day following therapy but should not be used as a predictor of OTC concentrations 96 h after treatment. Dairy producers should consult with their veterinarian to develop strategies that will prevent the presence of violative residues of OTC in bulk tank milk following intrauterine therapy
Phase diagram of the one-dimensional Holstein model of spinless fermions
The one-dimensional Holstein model of spinless fermions interacting with
dispersionless phonons is studied using a new variant of the density matrix
renormalisation group. By examining various low-energy excitations of finite
chains, the metal-insulator phase boundary is determined precisely and agrees
with the predictions of strong coupling theory in the anti-adiabatic regime and
is consistent with renormalisation group arguments in the adiabatic regime. The
Luttinger liquid parameters, determined by finite-size scaling, are consistent
with a Kosterlitz-Thouless transition.Comment: Minor changes. 4 pages, 4 figures. To appear in Physical Review
Letters 80 (1998) 560
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