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Biomedical subjects

A Ting

Publications and source records attributed to A Ting.

At least 19 recordsLinked to original sources
PubMed2000

Stable laser-pulse propagation in plasma channels for GeV electron acceleration

To achieve multi-GeV electron energies in the laser wakefield accelerator (LWFA) it is necessary to propagate an intense laser pulse long distances in plasma without disruption. A 3D envelope equation for a laser pulse in a tapered plasma channel is derived, which includes wakefields and relativistic and nonparaxial effects, such as finite pulse length and group velocity dispersion. It is shown that electron energies of approximately GeV in a plasma-channel LWFA can be achieved by using short pulses where the forward Raman and modulation nonlinearities tend to cancel. Further energy gain can be achieved by tapering the plasma density to reduce electron dephasing.

Journal Article↗
PubMed2000

Expert system assisted pharmacophore identification

An expert system for automatic perception of pharmacophoric groups is presented. Important features include consideration of the protonation state at physiological pH and detection of potential tautomerism. This perception information is used in the generation of pharmacophores using clique detection.

Journal Article↗
PubMed2000

Transverse modulation of an electron beam generated in self-modulated laser wakefield accelerator experiments

Low energy electron beams (E approximately 300 keV) generated in a self-modulated laser wakefield accelerator experiment were observed to filament and be deflected away from the laser axis forming radial jets in the electron beam profile. At higher energies (E>900 keV), the filamentation and jets were suppressed and smooth electron beams copropagating with the laser were observed. The observed electron beam filamentation likely results from laser beam filamentation in the plasma due to relativistic self-focusing effects. The radial jets of low energy electrons are likely caused by transverse ejection of the electrons due to the radial structure of the wakefield and space charge deflection of electrons as they exit the laser focus.

Journal Article↗
PubMed2000

Relativistic focusing and ponderomotive channeling of intense laser beams

The ponderomotive force associated with an intense laser beam expels electrons radially and can lead to cavitation in plasma. Relativistic effects as well as ponderomotive expulsion of electrons modify the refractive index. An envelope equation for the laser spot size is derived, using the source-dependent expansion method with Laguerre-Gaussian eigenfunctions, and reduced to quadrature. The envelope equation is valid for arbitrary laser intensity within the long pulse, quasistatic approximation and neglects instabilities. Solutions of the envelope equation are discussed in terms of an effective potential for the laser spot size. An analytical expression for the effective potential is given. For laser powers exceeding the critical power for relativistic self-focusing the analysis indicates that a significant contraction of the spot size and a corresponding increase in intensity is possible.

Journal Article↗
PubMed2000

Thoracoabdominal compression and respiratory system compliance in HIV-infected infants.

The thoracoabdominal compression technique (TAC) is used to measure expiratory flow in infants. We investigated whether TAC caused a change in total thoracic compliance (Crs), resistance (Rrs), and respiratory system time constant (Trs). We studied 41 infants (mean age, 12.4 mo; SD, 7.5) from five centers studying longitudinal lung and cardiovascular function of infants from HIV-infected mothers. We measured Crs, Rrs, and Trs before and after TAC. Changes in Crs, Rrs, and Trs after TAC were not dependent on the length of time since TAC. Crs and Trs were reduced after TAC, p = 0.013 and p = 0.003, respectively, whereas Rrs did not change. When compared with uninfected infants, HIV-infected infants had a larger post-pre TAC percent decline in Crs (p = 0.003) and a post-pre TAC rise in mean Rrs (p = 0.03). These differences remained significant after adjusting for sex and age. When performing infant pulmonary function testing, TAC itself produces a temporary decrease in Crs and Trs that is more significant in infants at risk for abnormal lung volume or compliance. Therefore, the sequence of performing the infant lung function parameters should be the same each time the testing is repeated with TAC as the last parameter tested at each testing session.

Abdomen↗
PubMed2000

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Journal Article↗
PubMed1999

Is laparoscopic approach to lumbar spine fusion worthwhile?

BACKGROUND: Laparoscopic lumbar spine fusion has been recently described. The aim of this study is to evaluate the safety and efficacy of this procedure for single- and multiple-level degenerative disc disease. METHODS: Twenty-four consecutive laparoscopic interbody lumbar fusions were evaluated prospectively (18 single-level were compared with 6 multiple-level procedures). Results of the laparoscopic multiple-level procedures were further compared with 12 open multiple-level operations. RESULTS: Twenty procedures were completed laparoscopically. The conversions were related to iliac vein lacerations (3 cases) and a mesenteric tear. Single-level cases had lower morbidity (22% versus 83%), shorter hospital stay (2 versus 10 days), and higher fusion rate (88% versus 50%) than multiple-level procedures. Overall results in the latter group were worse than in the matched open group. CONCLUSIONS: Laparoscopic single-level fusion (L5-S1) is safe and carries the benefits of minimal access surgery. Morbidity after multiple level approach is high, and this procedure cannot be advocated at this time.

Adult↗
PubMed1998

Alveolar vascularization of the lung in a lamb model of congenital diaphragmatic hernia.

Pulmonary hypoplasia and pulmonary hypertension are factors limiting the survival of infants with congenital diaphragmatic hernia (CDH). A reduction in the number of pre-acinar pulmonary vessels and increased muscularization are the structural lesions implicated as causes of irreversible hypoxemia. Whether there is a reduction in the number of air-blood barriers, which represent the capillary surface area of the lung involved in gas exchange, is unknown. We sought to determine if the lungs of CDH lambs have: (1) a reduction in total capillary surface area proportionate to the reduction in the total alveolar surface area of the lung; and/or (2) a disproportionate reduction in the number of capillaries (air blood barriers) within each acinus. The latter measurement was determined by calculating the capillary load which we defined as the number of air blood barriers/unit of surface density. At 80 d gestation (pseudoglandular period), a diaphragmatic hernia was created surgically in one lamb fetus of a twin gestation. At term, the fetuses were removed, the chests opened and the lungs fixed by a tracheal infusion of 1.5% glutaraldehyde at 25 cm of water pressure. Tissues from the lower lobes were examined by light and electron microscopy. Using computerized interactive morphometry, alveolar and capillary surface area, and capillary load were determined by intersection and point counting for the right and left lungs. The data show that the total alveolar surface area of the left CDH and control lungs were 1.8 +/- 0.8 m2 and 6.1 +/- 1.1 m2 (p < 0.01), respectively, and for the right CDH and control lungs 2.5 m2 +/- 0.1 and 11.2 +/- 1.9 m2 (p < 0.01), respectively. The total capillary surface area for the left CDH and control lungs were 0.7 +/- 0.3 m2 and 2.8 +/- 1.2 m2 (p < 0.05), respectively, and for the right CDH and control lungs 0.9 +/- 0.3 m2 and 3.8 +/- 1.5 m2 (p < 0.05), respectively. The capillary load was not statistically different. These findings demonstrate that the lungs in CDH are deficiently vascularized at the alveolar surface due to a reduction in the total alveolar surface area. Each acinus contains the same number of air blood barriers per unit of alveolar surface area indicating a normal acinar composition.

Animals↗
PubMed1996

Risk factors for the development of obliterative bronchiolitis after lung transplantation.

BACKGROUND: Acute rejection has emerged as an important risk factor for obliterative bronchiolitis after lung transplantation. We performed a multivariate analysis to assess the impact of additional variables. METHODS: Seventy-four recipients (48 heart-lung, 18 single-lung, and 8 bilateral-lung recipients) who survived longer than 90 days and underwent transplantation more than 15 months before data analysis were included in this study. Several variables were entered into a Cox regression analysis to determine their association with the development of bronchiolitis obliterans syndrome. RESULTS: Bronchiolitis obliterans syndrome developed in 48 (65%) of 74 patients. Significant correlations were detected for acute rejection score, defined as the sum of pathologic grades of each separate acute rejection episode (p = 0.0004, likelihood ratio test value = 12.4) and for lymphocytic bronchiolitis (p = 0.03). In a bivariate model, episodes of organizing pneumonia and bacterial or fungal pneumonia significantly increased the likelihood ratio test value of the acute rejection score. The addition of the cytomegalovirus infection score, reflecting the frequency and severity of infection, to the combination of the acute rejection score and episodes of bacterial or fungal pneumonia resulted in a further significant increase in the likelihood ratio test value. Significant risk factors for moderate to severe stages of airflow limitation were at least one episode of acute rejection of grade > or = 2, younger recipient age, and any acute rejection episode 180 days or longer after transplantation. CONCLUSIONS: Increasing frequency and severity of acute rejection episodes are strongly associated with the development of bronchiolitis obliterans syndrome. Lymphocytic bronchiolitis appeared to be significant by univariate analysis, but in a two-risk factor model, it did not augment the influence of acute rejection. Organizing pneumonia, bacterial or fungal pneumonia, and increasing severity and frequency of cytomegalovirus infections potentiate the effect of acute rejection. Late episodes of acute rejection and younger recipient age increase the risk for development of advanced disease.

Adolescent↗
PubMed1993

Clinical and socioeconomic benefits of serological HLA-DR matching for renal transplantation over three eras of immunosuppression regimens at a single unit.

The efficacy of HLA-DR matching in cadaveric renal transplantation is controversial in the cyclosporine (CsA) era. Reports have questioned both the reliability of serological HLA-DR typing as well as the benefit of matching in terms of improved graft survival. Analysis of 1,000 consecutive cadaver donor transplants performed at Oxford between 1975 and 1992 has shown that with improved immunosuppressive regimens and increased transplant success there has been a steadily diminishing influence of HLA-DR matching measured in terms of first graft outcome. For patients treated with azathioprine and prednisolone (n = 278) overall one-year first graft survival was 65%, but there was a 20% improvement associated with HLA-DR matching which has been maintained for up to 15 years. With the introduction of CsA, used either alone or in conjunction with low dose steroids (n = 96), one-year first graft survival was 69% and the difference between HLA-DR-matched and -mismatched transplants was 14%. Our current maintenance immunosuppressive protocol is triple therapy (N = 425) with an 81% one-year first graft survival for both matched and mismatched transplants. However, we do continue to find a marked correlation between HLA-DR matching and clinical course. HLA-DR-mismatched patients suffer more rejection episodes, spend a longer time in the hospital, and have higher creatinine levels at 3 months. This costs, on average, an extra 1,500 pounds for each mismatched transplant. The effect is most apparent in unsensitized males. For cadaveric regrafts, one-year graft survival for patients on triple therapy is 80% (n = 116) which does not differ from first graft survival rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Graft Rejection↗
PubMed1991

Production and characterization of human monoclonal lymphocytotoxic autoantibodies from a renal dialysis patient.

We have produced human monoclonal lymphocytotoxic autoantibodies from a renal dialysis patient by the generation of a mouse/human heterohybridoma. The antibodies are of the IgM class and react with the patient's autologous cells, the B-lymphoblastoid cell line producing the antibody, normal T and B lymphocytes, B cells from chronic lymphatic leukemia patients (CLL cells), and the autoantibody-sensitive cell line K562. Screening of the monoclonal antibodies (mAb) against panels of normal T and B cells and CLL cells demonstrated that different reactivity profiles could be generated at different dilutions of the mAb. These profiles were identical to those seen with autoantibodies from different renal patients and this suggests that these profiles do not imply different antibody specificities but differing target cell sensitivity. Reactivity profiles seen in the fluorescence binding assays suggest that the target cell sensitivity is dictated not by antigen density alone but also by antibody/antigen affinity. The results from studies of enzyme treatment of target cells and lectin inhibition of the molecular specificity suggest that the autoantibodies are polyreactive, capable of binding sialic acid-dependent epitopes and other negatively-charged cell surface molecules.

Animals↗