538 research outputs found
Exact Bayesian Analysis of Mixtures
In this paper, we show how a complete and exact Bayesian analysis of a
parametric mixture model is possible in some cases when components of the
mixture are taken from exponential families and when conjugate priors are used.
This restricted set-up allows us to show the relevance of the Bayesian approach
as well as to exhibit the limitations of a complete analysis, namely that it is
impossible to conduct this analysis when the sample size is too large, when the
data are not from an exponential family, or when priors that are more complex
than conjugate priors are used.Comment: 2 figures, 3 tables, 2 R codes. Chapter to appear in Mixtures:
Estimation and Application
A Quantile Variant of the EM Algorithm and Its Applications to Parameter Estimation with Interval Data
The expectation-maximization (EM) algorithm is a powerful computational
technique for finding the maximum likelihood estimates for parametric models
when the data are not fully observed. The EM is best suited for situations
where the expectation in each E-step and the maximization in each M-step are
straightforward. A difficulty with the implementation of the EM algorithm is
that each E-step requires the integration of the log-likelihood function in
closed form. The explicit integration can be avoided by using what is known as
the Monte Carlo EM (MCEM) algorithm. The MCEM uses a random sample to estimate
the integral at each E-step. However, the problem with the MCEM is that it
often converges to the integral quite slowly and the convergence behavior can
also be unstable, which causes a computational burden. In this paper, we
propose what we refer to as the quantile variant of the EM (QEM) algorithm. We
prove that the proposed QEM method has an accuracy of while the MCEM
method has an accuracy of . Thus, the proposed QEM method
possesses faster and more stable convergence properties when compared with the
MCEM algorithm. The improved performance is illustrated through the numerical
studies. Several practical examples illustrating its use in interval-censored
data problems are also provided
Fluid pressure penetration for advanced FEA of metal-to-metal seals
This numerical study investigates the behaviour of the contact faces in the metal-to-metal seal of a typical pressure relief valve in the commercial FE-package ANSYS. The valve geometry is simplified to an axisymmetric problem, which comprises a simple representative geometry consisting of only three components. A cylindrical nozzle, which has a valve seat on top, contacts with a disk, which is preloaded by a compressed linear spring. Analysis considerations include the effects of the Fluid Pressure Penetration (FPP) across the valve seat which exists at two different scales. In-service observations show that there is certain limited fluid leakage through the valve seat at operational pressures about 90% of the set pressure, which is caused by the fluid penetrating into surface asperities at the microscale. At the macroscale, non-linear FE-analysis using the FPP technique available in ANSYS revealed that there is also a limited amount of fluid penetrating into gap, which is caused primarily by the global plastic deformation of the valve seat. Accurate prediction of the fluid pressure profile over the valve seat is addressed in this study by considering the FPP interaction on both scales. The shape of this pressure profile introduces an additional component of the spring force, which needs to be considered to provide a reliable sealing
Effect of high temperature on structural behaviour of metal-to-metal seal in a pressure relief valve
This paper presents a numerical study involving the deformation of contact faces for a metal-to-metal seal in a typical pressure relief valve. The valve geometry is simplified to an axisymmetric problem, which comprises a simple geometry consisting of only three components: A cylindrical nozzle; which is in contact with a disc (representing the valve seat on top); which is preloaded by a compressed linear spring. The nozzle-disk pair is made of the austenitic stainless steel AISI type 316N(L) steel, which is typically used for power plant components. In a previous study, the macro-micro interaction of Fluid Pressure Penetration (FPP) was carried out in an iterative manual procedure at a temperature of 20°C. This procedure is now automated and implemented through an APDL script, which adjusts the spring force according to the current depth of FPP at a macroscale to maintain a consistent seal at elevated temperatures. Based upon the obtained results, specific suggestions to improve the leak tightness of the metal-to-metal seals at elevated temperatures are formulated
Artificial Intelligence and Location Verification in Vehicular Networks
Location information claimed by devices will play an ever-increasing role in
future wireless networks such as 5G, the Internet of Things (IoT). Against this
background, the verification of such claimed location information will be an
issue of growing importance. A formal information-theoretic Location
Verification System (LVS) can address this issue to some extent, but such a
system usually operates within the limits of idealistic assumptions on a-priori
information on the proportion of genuine users in the field. In this work we
address this critical limitation by using a Neural Network (NN) showing how
such a NN based LVS is capable of efficiently functioning even when the
proportion of genuine users is completely unknown a-priori. We demonstrate the
improved performance of this new form of LVS based on Time of Arrival
measurements from multiple verifying base stations within the context of
vehicular networks, quantifying how our NN-LVS outperforms the stand-alone
information-theoretic LVS in a range of anticipated real-world conditions. We
also show the efficient performance for the NN-LVS when the users' signals have
added Non-Line-of-Site (NLoS) bias in them. This new LVS can be applied to a
range of location-centric applications within the domain of the IoT.Comment: 6 Pages, 5 figure
Study of mechanical aspects of leak tightness in a pressure relief valve using advanced FE-analysis
This paper presents a numerical study involving the deformation of contact faces in the metal-to-metal seal in a typical pressure relief valve. The valve geometry is simplified to an axisymmetric problem, which comprises a simple geometry consisting of only 3 components. A cylindrical nozzle, which has a valve seat on top, contacts with a disk, which is preloaded by a compressed linear spring. All the components are made of AISI type 316N(L) steel defined using the multilinear kinematic hardening model based on monotonic and cyclic tests at 20°C. In-service observations show that there is a limited fluid leakage through the valve seat at operational pressures about 90% of the set pressure, which is caused by the fluid penetrating into surface asperities at the microscale. Nonlinear FEA in ANSYS using the fluid pressure penetration (FPP) technique revealed that there is a limited amount of fluid penetrating into gap, which is caused by the plastic deformation of the valve seat at the macroscale. Prediction of the fluid pressure distribution over the valve seat just before the valve lift is addressed in this study considering the FPP interaction on multiscale. This is the principal scope, since it allows adjustment of the valve spring force in order to improve the leak tightness
Issues in modern bone histomorphometry
This review reports on proceedings of a bone histomorphometry session conducted at the Fortieth International IBMS Sun Valley Skeletal Tissue Biology Workshop held on August 1, 2010. The session was prompted by recent technical problems encountered in conducting histomorphometry on bone biopsies from humans and animals treated with anti-remodeling agents such as bisphosphonates and RANKL antibodies. These agents reduce remodeling substantially, and thus cause problems in calculating bone remodeling dynamics using in vivo fluorochrome labeling. The tissue specimens often contain few or no fluorochrome labels, and thus create statistical and other problems in analyzing variables such as mineral apposition rates, mineralizing surface and bone formation rates. The conference attendees discussed these problems and their resolutions, and the proceedings reported here summarize their discussions and recommendations
Evaluation of immunogenicity and efficacy of Fasciola hepatica Tetraspanin 2 (TSP2) fused to E. coli Heat-Labile Enterotoxin B Subunit LTB adjuvant following intranasal vaccination of cattle
Fasciolosis, caused by the liver flukes Fasciola hepatica and F. gigantica, is an economically important and globally distributed zoonotic disease. Liver fluke infections in livestock cause significant losses in production and are of particular concern to regions where drug resistance is emerging. Antigens of the F. hepatica surface tegument represent promising vaccine candidates for controlling this disease. Tetraspanins are integral tegumental antigens that have shown partial protection as vaccine candidates against other trematode species. The Escherichia coli heat-labile enterotoxin’s B subunit (LTB) is a potent mucosal adjuvant capable of inducing an immune response to fused antigens. This study investigates the potential of F. hepatica tetraspanin 2 extracellular loop 2 (rFhTSP2) as a protective vaccine antigen and determines if fusion of FhTSP2 to LTB can enhance protection in cattle. Cattle were immunised subcutaneously with rFhTSP2 mixed in the Freund’s adjuvant and intranasally with rLTB-FhTSP2 in saline, accounting for equal molar ratios of tetraspanin in both groups. Vaccination with rFhTSP2 stimulated a strong specific serum IgG response, whereas there was no significant serum IgG response following rLTB-FhTSP2 intranasal vaccination. There was no substantial antigen specific serum IgA generated in all groups across the trial. Contrastingly, after the fluke challenge, a rise in antigen specific saliva IgA was observed in both vaccination groups on Day 42, with the rLTB-FhTSP2 vaccination group showing significant mucosal IgA production at Day 84. However, neither vaccine group showed a significant reduction of fluke burden nor faecal egg output. These results suggest that intranasal vaccination with rLTB-FhTSP2 does elicit a humoral mucosal response but further work is needed to evaluate if mucosal delivery of liver fluke antigens fused to LTB is a viable vaccine strategy
Evaluation of Immunogenicity and Efficacy of Fasciola hepatica Tetraspanin 2 (TSP2) Fused to E. coli Heat-Labile Enterotoxin B Subunit LTB Adjuvant Following Intranasal Vaccination of Cattle
Fasciolosis, caused by the liver flukes Fasciola hepatica and F. gigantica, is an economically important and globally distributed zoonotic disease. Liver fluke infections in livestock cause significant losses in production and are of particular concern to regions where drug resistance is emerging. Antigens of the F. hepatica surface tegument represent promising vaccine candidates for controlling this disease. Tetraspanins are integral tegumental antigens that have shown partial protection as vaccine candidates against other trematode species. The Escherichia coli heat-labile enterotoxin’s B subunit (LTB) is a potent mucosal adjuvant capable of inducing an immune response to fused antigens. This study investigates the potential of F. hepatica tetraspanin 2 extracellular loop 2 (rFhTSP2) as a protective vaccine antigen and determines if fusion of FhTSP2 to LTB can enhance protection in cattle. Cattle were immunised subcutaneously with rFhTSP2 mixed in the Freund’s adjuvant and intranasally with rLTB-FhTSP2 in saline, accounting for equal molar ratios of tetraspanin in both groups. Vaccination with rFhTSP2 stimulated a strong specific serum IgG response, whereas there was no significant serum IgG response following rLTB-FhTSP2 intranasal vaccination. There was no substantial antigen specific serum IgA generated in all groups across the trial. Contrastingly, after the fluke challenge, a rise in antigen specific saliva IgA was observed in both vaccination groups on Day 42, with the rLTB-FhTSP2 vaccination group showing significant mucosal IgA production at Day 84. However, neither vaccine group showed a significant reduction of fluke burden nor faecal egg output. These results suggest that intranasal vaccination with rLTB-FhTSP2 does elicit a humoral mucosal response but further work is needed to evaluate if mucosal delivery of liver fluke antigens fused to LTB is a viable vaccine strategy
Glutamate and Dysconnection in the Salience Network: Neurochemical, Effective Connectivity, and Computational Evidence in Schizophrenia
Background: Functional dysconnection in schizophrenia is underwritten by a pathophysiology of the glutamate neurotransmission that affects the excitation-inhibition balance in key nodes of the salience network. Physiologically, this manifests as aberrant effective connectivity in intrinsic connections involving inhibitory interneurons. In computational terms, this produces a pathology of evidence accumulation and ensuing inference in the brain. Finally, the pathophysiology and aberrant inference would partially account for the psychopathology of schizophrenia as measured in terms of symptoms and signs. We refer to this formulation as the 3-level hypothesis. Methods: We tested the hypothesis in core nodes of the salience network (the dorsal anterior cingulate cortex [dACC] and the anterior insula) of 20 patients with first-episode psychosis and 20 healthy control subjects. We established 3-way correlations between the magnetic resonance spectroscopy measures of glutamate, effective connectivity of resting-state functional magnetic resonance imaging, and correlations between measures of this connectivity and estimates of precision (inherent in evidence accumulation in the Stroop task) and psychopathology. Results: Glutamate concentration in the dACC was associated with higher and lower inhibitory connectivity in the dACC and in the anterior insula, respectively. Crucially, glutamate concentration correlated negatively with the inhibitory influence on the excitatory neuronal population in the dACC of subjects with first-episode psychosis. Furthermore, aberrant computational parameters of the Stroop task performance were associated with aberrant inhibitory connections. Finally, the strength of connections from the dACC to the anterior insula correlated negatively with severity of social withdrawal. Conclusions: These findings support a link between glutamate-mediated cortical disinhibition, effective-connectivity deficits, and computational performance in psychosis
- …