4,596 research outputs found
Network-based approach to Korean handwriting analysis
No full textIt is well known that the stochastic approach using the HMM and dynamic programming-based search is particularly suited to the analysis of time series signals including on-line handwriting. The starting point of this research is a network of HMMs which models the whole set of characters. Then it is followed by the assertion that the HMM for the on-line script can be applied to not only on-line character recognition but also to the handwriting synthesis and even pen-trajectory recovery in off-line character images. The solutions to these problems are based on the single network of HMMs and the single principle of DP-based state-observation alignment. Given an observation sequence, the search for the best path in the network corresponds to the recognition. Given a character model, the search for the best observation sequence corresponds to the handwriting generation. The proposed framework has been shown to work nicely through a set of tests on Korean characters
Ligature modeling for online cursive script recognition
No full textOnline recognition of cursive words is a difficult task owing to variable shape and ambiguous letter boundaries. The approach proposed in this paper is based on hidden Markov modeling of letters and inter-letter patterns called ligatures occurring in cursive script. For each of the letters and the ligatures we create one HMM that models temporal and spatial variability of handwriting. By networking the two kinds of HMMs, we can design a network model for all words or composite characters. The network incorporates the knowledge sources of grammatical and structural constraints so that it can better capture the characteristics of handwriting. Given the network, the problem of recognition is formulated into that of finding the most likely path from the start node to the end node. A dynamic programming-based search for the optimal input-network alignment performs character recognition and letter segmentation simultaneously and efficiently. Experiments on Korean character showed correct recognition of up to 93.3 percent on unconstrained samples. It has also been compared with several other schemes of HMM-based recognition to characterize the proposed approach
Suppression of GHz, range power/ground inductive impedance and simultaneous switching noise using embedded film capacitors in multilayer packages and PCBs
No full textWe measured and demonstrated the great advantages of embedded film capacitors in reducing power/ground inductive impedance and the suppression of SSN at frequencies up to 3 GHz for high-performance multilayer packages and PCBs. Eight-layer test PCBs were fabricated, and their inductive power/ground network impedances were measured as a function of film thickness, via distribution, and combined use with discrete decoupling capacitors, using a two-port self-impedance measurement method. This successfully demonstrated that the power/ground inductive impedance was reduced from 270 pH to 106 pH simply by using an embedded film capacitor instead of 16 discrete decoupling capacitors
INSITU ESTIMATION OF AN ACOUSTIC SOURCE IN AN ENCLOSURE AND PREDICTION OF INTERIOR NOISE BY USING THE PRINCIPLE OF VIBROACOUSTIC RECIPROCITY
No full textThe volume velocity of an acoustic source can be widely used in determining the vibroacoustic transfer functions, in measuring the acoustic transfer impedances, and in finding the generated power of an acoustic source. Several techniques utilizing special experimental devices have been proposed for this purpose, including the laser velocimetry, the internal pressure measurement, and the face-to-face electroacoustic measurement. However, for a source in an enclosure with flexible walls, the vibroacoustic coupling should be considered, especially in the case of a loudspeaker source that has low internal mechanical impedance. The present method, which uses the principle of vibroacoustic reciprocity, can give a reasonable estimation of the transfer functions and can be used in determining the volume velocity of a source in situ. Because the present method does not require a special facility or the information on the source surface vibration, the method can be applied to any irregularly shaped source in a flexible enclosure. With the obtained vibroacoustic transfer functions, the interior noise field in an enclosure can be predicted by vectorial summation when the boundary points are excited by uncorrelated dynamic forces. The predicted internal pressure in an enclosure is in good agreement with the measured internal pressure even in the presence of sound absorbers inside the enclosure
Characterizing determinants of BK Polyomavirus-specific immune response
No full textBK polyomavirus (BKPyV) is one of now 13 human polyomavirus (HPyV) species detected in humans. BKPyV is only known to infect humans and seroprevalence rates of more than 90% have been reported in adult populations around the world. Following primary infection, BKPyV persists in the renourinary tract without causing any disease as evidenced by urinary shedding in 5% - 10% of healthy immunocompetent blood donors.
In immunocompromised persons, however, BKPyV can cause significant diseases whereby uncontrolled high-level replication may lead to organ invasive pathologies in kidneys, bladder, lungs, vasculature, and the central nervous system. The most consistently found diseases are BKPyV-associated hemorrhagic cystitis (BKPyVHC) in 5%-20% allogeneic hematopoietic stem cells transplant patients, and BKPyV-associated nephropathy (BKPyVAN) in 1%-15% of kidney transplant patients. BKPyVHC is highly symptomatic with pain, anemic bleeding, and increased mortality. BKPyVAN is asymptomatic except for progressive renal failure and premature return to dialysis. Both entities are characterized by high-level viral replication i.e. with urine BKPyV loads of 8-10 log10 Geq/mL, plasma BKPyV loads often above 4 log10 Geq/mL, and an allogeneic constellation between the virus-infected host cell and the available T-cell effectors. Despite these similarities, the clinical manifestations are strikingly different suggesting relevant, but experimentally undefined differences in pathogenesis. Thus, BKPyVHC typically occurs within 4 weeks after allogeneic HSCT and is confined to the bladder, and typically without kidney involvement. By contrast, BKPyVAN is diagnosed around 3-6 months after kidney transplantation and confined to the kidney allograft without causing cystitis. Although high-level BKPyV replication should be formally amenable to antiviral drug treatment, no effective and BKPyV-specific antiviral therapy is currently available. Therefore, a better understanding of the immune alteration in both diseases has been deemed essential to identify patients at risk and to develop prophylactic, preemptive and therapeutic strategies.
The currently recommended strategy for BKPyVAN is to screen kidney transplant patients for BKPyV replication and to promptly reduce immunosuppressive therapy in those with significant replication to facilitate mounting of BKPyV-specific T cell responses and thereby preventing progression to disease. This manoeuver has been linked to expanding BKPyV-specific T cell responses in the peripheral blood of kidney transplant patients. However, this approach may place patients at risk for acute rejection episodes that predispose equally well to premature kidney transplant failure. Although the clinical feasibility of reducing immunosuppression and curtailing BKPyV replication has been shown to be effective in prospective cohort studies for many, but not all of kidney transplant patients, this approach has not been possible in allogeneic HSCT patients because of concurrent or imminent graft-versus host disease. Thus, there are significant gaps in the current understanding of the BKPyV– host interaction in the normal host and in the allogeneic setting, which need to be investigated for a more effective and safer management of these significant viral complications.
In this thesis, the interaction of BKPyV and the immune response has been approached from two different angles. In the first project, potential mechanisms of BKPyV immune evasion were studied. Here, we focused on a small accessory protein called agnoprotein encoded as a leader protein in the late viral early region (LVGR). Although HPyV genomes overall show a very similar genome organization, agnoproteins are only found in the genomes of BKPyV and JCPyV that have a kidney tropisms, but not in any of the other 11 presumably non-renotropic HPyVs. We hypothesized that agnoprotein could play a role in immune evasion by downregulating HLA expression. The effects of agnoprotein were studied on HLA class I and II expression in vitro by flow cytometry following transfection of primary human renal tubular epithelial cells, which are the viral target of BKPyV-associated nephropathy. In addition, transfected human UTA-6 cells were studied as well as UTA-6 cells bearing a tetracycline-regulated agnoprotein. As control, the effects were compared with the ICP47 protein of Herpes simplex virus-1, which has been previously reported to effectively down-regulate HLA class I. Although both viral proteins share some similarities at the protein level, our results showed that BKPyV agnoprotein did not down-regulate HLA class I or class II molecules. Also, there was not inhibitory effect on the increase of HLA-class I or class-II surface expression following exposure to interferon-. By contrast, ICP47 reduced HLA class I surface expression, but not class II. We also evaluated effects of agnoprotein on virus epitope-specific T-cell killing by 51Chromium release assay, however no interference could be observed. We concluded that agnoprotein did not contribute to these types of HLA-dependent immune evasion processes. However, further investigations are needed to understand if agnoprotein could contribute to viral immune escape by other mechanisms.
In the second project, we aimed at better characterizing BKPyV-specific CD8 T cell immunity targeting epitopes encoded in the early viral gene region (EVGR). Selected coding sequences of the BKPyV EVGR were submitted to two web-based computer algorithms (SYFPEITHI, IEDB) in order to predict immunodominant 9mer epitopes presented by 14 frequent HLA-class I molecules. For an experimental confirmation, 97 different 9mer epitopes were chemically synthesized and tested in 42 healthy individuals. A total of 39 epitopes could be confirmed by interferon- ELISpot assay in at least 30% of healthy individuals. Interestingly, most of the 9mer epitopes appeared to cluster in short amino acid stretches, and some 9mer could be presented by more than one HLA class I allele as expected for immunodominant domains. HLA-specific presentation was demonstrated by 9mer- MHC-I streptamers for 21/39 (54%) epitopes. The 9mer dependent T-cell killing by 51Chromium release assay and the CD107a surface detection indicated that the 9mer epitopes could be recognized by cytotoxic T-cells. Moving to a clinically relevant situation, 13 9mer epitopes could be validated in 19 kidney transplant patients protected from, or recovering from, BKPyV viremia. The results suggest that, pending further corroboration in larger patient populations, novel 9mer epitopes can be identified, which are associated with CD8 T cell control of BKPyV replication. Thus the identified immunodominant 9mer T-cell epitopes could be further developed for clinical assays to better predict the risk and the recovery of BKPyV diseases, help guiding immunosuppression reduction, and to develop specific adoptive T-cell therapy or vaccine responses to prevent or treat BKPyV-associated disease
In vitro and in vivo characterization of the cytomegalovirus and polyomavirus BK specific immune response
No full textDuring my PhD thesis several aspects of the interaction of Cytomegalovirus
and Polyomavirus BK with the host’s immune system were examined (see list
of publications). The overall aim was to compare immune response in healthy
individuals and kidney transplant recipients with or without viral replication.
In healthy individuals, Polyomaviruses BK and JC infect 80% and 60%,
respectively. For CMV seroprevalences may reach up to 80%. Intermittent
virus shedding in urine is observed for BKV in 7%, JCV in 19% and CMV in
0%. However, no virus replication in plasma was detected. Posttransplant,
mainly due to prolonged immune suppression the amount and function of
CMV- and BKV-specific T-cells is impaired. Calcineurin inhibitors lead to a
direct reduction of INFγ production of virus-specific T-cells, whereas antiproliferative
immunosuppressives reduce the expansion capacity in a dosedependent
manner. This may be a major reason for uncontrolled virus
replication.
The humoral response reflects the amount of recent antigen exposure and
does not directly indicate protection from virus replication. Virus-specific
cellular immune responses would probably allow to assessing the risk of
future replication.
Overall the importance of CMV and BKV specific T-cells posttransplant in
controlling virus replication was examined. For both viruses we could
calculate a protective threshold of virus-specific T-cells. CMV-pp65 specific
CD4 T-cells above 0.03% were significantly associated with no CMV
replication during the next eight weeks. Additionally, below this cut-off, CMV
seropositive recipients developed more often GCV-resistant CMV replication.
During BKV replication, patients with more than 69 BKV-LT specific T-cells
per 1 Mio PBMCs were significantly more often showing decreasing BKV
loads in plasma. As virus-specific T-cells seem to be crutial in reducing virus replication, and
reduction of immune suppression harbours the risk of acute rejection, a
booster vaccine could be a new therapeutic option. A booster vaccine could
probably elevate the amount of virus-specific T-cells above a critical threshold
of protection from disease, despite effects of immune suppression.
We tried to identify immunodominant regions with the CMV pp65 and BKV LT
proteins. We used a combined approach of computer prediction algorithms
and experimental verification. Epitope mapping of BKV LT with computer
prediction revealed several clusters, which could be immunodominant and
also potentially be processed and recognized in various HLA backgrounds.
The identified cluster regions were synthesised as 15 and 25mers. Expansion
and re-stimulation with predicted epitopes could so far confirm the HLA A and
B-specific prediction of single 9mers covered by the larger 15 and 25mer
sequences. However, other HLA types need to be tested for direct stimulation
and expansion potential of the predicted epitopes. Additionally, tetramer
staining should be performed for verification.
Based on this research, we will be able to improve current immune monitoring
and probably a high-specific peptide-based vaccine against BKV LT could be
developed and be used to increase the amount of BKV-LT specific T-cells.
Another potentially therapeutic agent could be the blockade of PD1 ligand.
PD1 expression in chronic virus infection lead to impaired CD8+ T-cell
function. CMV-specific CD4 T-cells treated with an inhibitory antibody against
PD1 ligand, and thereby activating CD4+ T-cells, lead to a increase of the
expansion capacity. We have shown, that the anti-PD1 ligand antibody
increases various cytokines. This could be also tested for BK virus.
Measurement of virus-specific T-cells may replace serological assays in the
future, due to a better correlation to effective antiviral control, which can be
used as monitoring tool during infection and post-vaccination
Use of Hilbert Transform for Priority Determination of Partially Correlated Inputs in Source Identification via MISO Modeling
No full textOn the reconstruction of the vibro-acoustic field over the surface enclosing an interior space using the boundary element method
No full textThe vibrational velocity, sound pressure, and acoustic power on the vibrating boundary comprising an enclosed space are reconstructed by the boundary element method based on the measured field pressures. The singular value decomposition is used to obtain the inverse solution in the least-square sense and to express the acoustic modal expansion between the measurement and source fields. In general, such an inverse operation has been considered an ill-posed problem having a divergence phenomenon involved with extremely small measurement errors. The ill-conditioned nature of the acoustic inverse problem is caused by the singularity of the transfer matrix which produces nonradiating wave components. In order to minimize the singularity and to also reduce the number of measurement points, optimal measurement positions are determined by the effective independence method. Regularization methods are used to stabilize the reconstructed field by suppressing nonradiating components resulting in the singular transfer matrix. In order to enhance the resolution of the reconstructed field, the optimal regularization order for yielding the minimum mean-square error is estimated from the known measurement noise variance by virtue of the statistical analysis. A half-scaled automotive cabin is considered an example for validating and demonstrating the proposed reconstruction process. It is noted that the present method can improve the resolution of the reconstructed field; thus vibro-acoustic parameters of the vibrating boundary can be estimated in reasonably good precision. (C) 1996 Acoustical Society of America
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