332 research outputs found
Purely radiative irrotational dust spacetimes
We consider irrotational dust spacetimes in the full non-linear regime which
are "purely radiative" in the sense that the gravitational field satisfies the
covariant transverse conditions div(H) = div(E) = 0. Within this family we show
that the Bianchi class A spatially homogeneous dust models are uniquely
characterised by the condition that is diagonal in the shear-eigenframe.Comment: 6 pages, ERE 2006 conference, minor correction
Purely radiative perfect fluids with degenerate shear tensor
We consider non-rotating geodesic perfect fluid spacetimes which are purely
radiative in the sense that the gravitational field satisfies the covariant
transverse conditions div H = div E = 0. We show that when the shear tensor S
is degenerate, H, E and S necessarily commute and hence the resulting
spacetimes are hypersurface homogeneous of Bianchi class A (modulo some purely
electric exceptions).Comment: 8 pages, references added, typos corrected, simplified some algebraic
manipulation
Motion correction of SPEC projection before reconstruction
In Single Photon Emission Computed Tomography (SPECT), the data acquisition occurs over a relatively long
time, typically in the range of 5-30 minutes. During this period, the patient must lie still to guarantee the image
quality. Nevertheless, patient movement has frequently been reported in clinical applications. This movement
causes misalignment of the projection frames, which degrades the reconstructed image and may introduce
artifacts. However, the ability to detect and correct for the motion using a computational method is valuable for
quality assurance of SPECT imaging.
In this work a correlation function based on Linogram and Sinogram of the projection is evaluated in order to
estimate the occurred motion and correct it for the best alignment.
By our implemented method the motion artifacts of our cases reduced considerably and our results showed that
the misalignment (motion) between the projections could be found with a small error depending on the
resolution of the images (pixel size), and the time and duration of the applied motion during the course of
projection acquisition
Detection and evaluation of damage in aircraft composites using electromagnetically coupled inductors
The paper presents a quantitative damage evaluation of carbon-fibre reinforced polymer (CFRP) plates using a non-contact electromagnetic (EM) sensor. The EM sensor with coupled spiral inductors (CSI) is employed here to detect both impact induced and simulated damage leading to an accurate evaluation of the location, depth and width of sub-surface defects. The effect of inspection frequency, standoff distance and signal power are also investigated leading to the development of an engineering circuit design tool that relates the set up and calibration of the sensor to its detection performance. It is found that the dynamic range of the transmission coefficient is the limiting factor in the original Salski CSI sensor and this problem is addressed by adding ferrite layers to reduce the reluctance of the magnetic circuit, improving damage sensing by 22%. The study leads to a further development of utilising an open ferrite yoke with a pair of encircling coils, which shows a 57% sensitivity improvement and clearer identification of air gaps (voids) and delamination in CFRP laminates. The proposed EM yoke design CSI sensor is low cost and could be assembled into an array for non-contact, in situ mechatronic scanning of aircraft composite wings
Intranasal administration of endometrial mesenchymal stem cells as a suitable approach for Parkinson�s disease therapy
This study aimed to investigate the therapeutic effects of intranasal administration of human endometrium-derived stem cells (HEDSCs) in the mouse model of Parkinson�s disease (PD). Thirty days after intrastriatal injection of 6-OHDA, HEDSCs were administrated intranasally in three doses (104, 5 � 104 and 105 cells µl�1). During 120 days after stem cell administration, behavioral tests were examined. Then the mice were sacrificed and the fresh section of the substantia nigra pars compacta (SNpc) was used for detection of HEDSCs-GFP labeled by fluorescence microscopy method. In addition, immunohistochemistry was used to assay GFP, human neural Nestin, and tyrosine hydroxylase (TH) markers in the fixed brain tissue at the SNpc. Our data revealed that behavioral parameters were significantly improved after cell therapy. Fluorescence microscopy assay in fresh tissue and GFP analysis in fixed tissue were showed that the HEDSCs-GFP labeled migrated to SNpc. The data from immunohistochemistry revealed that the Nestin as a differential neuronal biomarker was expressed in SNpc. Also, TH as a dopaminergic neuron marker significantly increased after HEDSCs therapy in an optimized dose 5 � 104 cells µl�1. Our results suggest that intranasal administration of HEDSCs improve the PD symptoms in the mouse model of PD dose-dependent manner as a noninvasive method. © 2019, Springer Nature B.V
Effects of Synaptic and Myelin Plasticity on Learning in a Network of Kuramoto Phase Oscillators
Models of learning typically focus on synaptic plasticity. However, learning
is the result of both synaptic and myelin plasticity. Specifically, synaptic
changes often co-occur and interact with myelin changes, leading to complex
dynamic interactions between these processes. Here, we investigate the
implications of these interactions for the coupling behavior of a system of
Kuramoto oscillators. To that end, we construct a fully connected,
one-dimensional ring network of phase oscillators whose coupling strength
(reflecting synaptic strength) as well as conduction velocity (reflecting
myelination) are each regulated by a Hebbian learning rule. We evaluate the
behavior of the system in terms of structural (pairwise connection strength and
conduction velocity) and functional connectivity (local and global
synchronization behavior). We find that for conditions in which a system
limited to synaptic plasticity develops two distinct clusters both structurally
and functionally, additional adaptive myelination allows for functional
communication across these structural clusters. Hence, dynamic conduction
velocity permits the functional integration of structurally segregated
clusters. Our results confirm that network states following learning may be
different when myelin plasticity is considered in addition to synaptic
plasticity, pointing towards the relevance of integrating both factors in
computational models of learning.Comment: 39 pages, 15 figures This work is submitted in Chaos: An
Interdisciplinary Journal of Nonlinear Scienc
Shearfree perfect fluids with solenoidal magnetic curvature and a gamma-law equation of state
We show that shearfree perfect fluids obeying an equation of state p=(gamma
-1) mu are non-rotating or non-expanding under the assumption that the spatial
divergence of the magnetic part of the Weyl tensor is zero.Comment: 11 page
Gaining comprehensive data about sexual knowledge through surveys
Background:
Delivery of sexual health services rely on rigorous facts extracted from surveys, but often those facts cannot be available due to the lack of culturally-sensitive questionnaires.
Objective:
our aim was to show the validity and reliability of the Persian version of the Acquisition of Sexual Information Test (ASIT), a measure selected due to its assemblages with Iranian culture.
Materials and Methods:
Forward-backward procedure was applied to translate the questionnaire. Cross-sectional study was carried out and psychometric properties of the Iranian version were tested in a thirty sample of reproductive-age women. Face validity was assessed by qualitative and quantitative methods. Content validity was also assessed by calculating two quantitative indicators as content validity index (CVI) and content validity ratio (CVR). Reliability was assessed by test-retest analyses.
Results:
Impact score was 1.5, the majority of participants (83.3%) stated that the overall level of questionnaire was high but some of the questions were irrelevant to sexual knowledge. Many questions (90%) gained a CVR less than 0.56, and all of them gained CVIs lower than 0.7. Correlation in test-retest reliability was 0.85
Purely radiative perfect fluids
We study `purely radiative' (div E = div H = 0) and geodesic perfect fluids
with non-constant pressure and show that the Bianchi class A perfect fluids can
be uniquely characterized --modulo the class of purely electric and
(pseudo-)spherically symmetric universes-- as those models for which the
magnetic and electric part of the Weyl tensor and the shear are simultaneously
diagonalizable. For the case of constant pressure the same conclusion holds
provided one also assumes that the fluid is irrotational.Comment: 12 pages, minor grammatical change
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Diagnostic Accuracy of Sixty Four Multi-Slice CT Angiography in Assessment of Arterial Cut-Off and Run-Off in Comparison with Surgical Findings
Background/Objective: The accurate anatomic mapping and determination of the severity of arterial disease, an important health problem of the elderly, is of great significance. We aimed to determine the diagnostic value of 64-multislice CT angiography (MSCTA) in run-off and cut-off sites of arterial disease. Patients and Methods: Throughout the study, MSCTA followed by an operative intervention was carried out on a total of 38 patients with clinical signs and symptoms suggestive of arterial disease (AD) all of whom had the indication for vascular surgery. The mean age of patients was 34±15.86 (range, 23 to 93) years. MSCTA was executed using a 64-slice CT scanner, during the arterial phase of injecting the nonionic, contrast medium with a power injector at the rate of 5 ml/sec into the antecubital vein and exploration and revascularization of peripheral arterial disease was performed intraoperatively. Results: Atherosclerosis and arterial disease, the most common causes of vascular occlusion, were more common in the lower extremities. According to MSCTA findings, the most frequent site of stenosis was the superficial femoral artery. Spearman’s correlation coefficient showed a high degree of agreement amongst the raters. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and the accuracy of MSCTA compared to surgery were 83.8%, 96%, 96.8%, 81.3% and 89%, respectively. MSCTA findings were compared with surgery as a standard of reference, which showed concordance in the majority of cases (81.6%). Cut-off sites were correctly identified by MSCTA in 97.3% of the patients and the most common sites of discordance were the run-off sites (18.2%). Conclusion: MSCTA angiography as a novel diagnostic modality may be a suitable alternative and a viable choice for routine clinical diagnosis
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