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R A Cairns

Publications and source records attributed to R A Cairns.

15 recordsLinked to original sources
PubMed2005

Efficiency and energy spread in laser-wakefield acceleration.

The theoretical limits on efficiency and energy spread of the laser-wakefield accelerator are investigated using a one-dimensional model. Modifications, both of the wakefield due to the electron bunch, and of the laser pulse shape due to the varying permittivity of the plasma, are described self-consistently. It is found that a short laser pulse gives a higher efficiency than a long laser pulse with the same initial energy. Energy spread can be minimized by optimizing bunch length and bunch charge such that the variation of the accelerating force along the length of the bunch is minimized. An inherent trade-off between energy spread and efficiency exists.

Journal Article↗
PubMed2003

Molecular mechanisms of tumor invasion and metastasis: an integrated view.

As tumors progress to increased malignancy, cells within them develop the ability to invade into surrounding normal tissues and through tissue boundaries to form new growths (metastases) at sites distinct from the primary tumor. The molecular mechanisms involved in this process are incompletely understood but those associated with cell-cell and cell-matrix adhesion, with the degradation of extracellular matrix, and with the initiation and maintenance of early growth at the new site are generally accepted to be critical. This article discusses current knowledge of molecular events involved in these various processes. The potential role of adhesion molecules (eg. integrins and cadherins) has undergone a major transition over the last ten years, as it has become apparent that such molecules play a major role in signaling from outside to inside a cell, thereby controlling how a cell is able (or not) to sense and interact with its local environment. Similarly the roles of proteolytic enzymes and their inhibitors (eg. matrix metalloproteinases and TIMPs) have also expanded as it has become apparent that they not only have the abilities to break down the components of the extracellular matrix but also are involved in the release of factors which can affect the growth of the tumor cells positively or negatively. Recent work has highlighted the importance of the later, post-extravasational stages of metastasis, where adhesion and proteolysis are now known to play a role along with other processes such as apoptosis, dormancy, growth factor-receptor interactions and signal transduction. Recent work has also demonstrated that not only the immediate cellular microenvironment, in terms of specific cell-cell and cell-matrix interactions, but also the extended cellular microenvironment, in terms of vascular insufficiency and hypoxia in the primary tumor, can modify cellular gene expression and enhance metastasis. Mechanisms of metastasis appear to involve a complex array of genetic and epigenetic changes many of which appear to be specific both for different types of tumors and for different sites of metastasis. Our improved understanding of the expanded roles of the individual molecules involved has resulted in a mechanistic blurring of the previously described discrete stages of the metastatic process.

Animals↗
PubMed2002

Role of parallel flow in the improved mode on the STOR-M tokamak.

A novel feature of the H-mode induced by compact torus injection on the STOR-M tokamak is observed. There is almost no change in the radial electric field profiles during and after the L-H transition. The usual hypothesis of the E x B shear stabilization mechanism is therefore unlikely to play a role in this transition. A new mechanism of the stabilization of microinstabilities by parallel flow is suggested as the plausible cause for the transition to this improved regime.

Journal Article↗
PubMed2001

Acute (cyclic) hypoxia enhances spontaneous metastasis of KHT murine tumors.

Hypoxia exists in most human and rodent solid tumors and has been shown to correlate with poor survival in carcinoma of the cervix, carcinoma of the head and neck, and soft tissue sarcoma. It exists both chronically, due to the poorly organized vasculature of solid tumors, and acutely, due to fluctuations in blood flow. It has been found that tumors that are more hypoxic are more likely to metastasize in humans and in rodent models, and it has been demonstrated that exposure of tumor cells to hypoxia in vitro can transiently enhance their metastatic potential when they are reinjected i.v. into mice. The purpose of the present study was to determine whether experimentally imposed hypoxic stress in vivo, either chronic or acute, affects the process of spontaneous metastasis in tumor-bearing mice. We exposed mice bearing KHT tumors to low oxygen conditions (5-7% O(2) breathing) daily during tumor growth in an attempt to induce additional chronic (2 h/day) and acute (12 x 10 min/day) hypoxia in their tumors. By monitoring tumor pO(2) levels over the course of treatment, we demonstrated that these treatments produce acute and chronic hypoxia within the tumor tissue. The acute but not the chronic hypoxia treatment significantly increased the number of spontaneous microscopic lung metastases in the mice by a factor of about 2, and the results suggest that this effect was due to the changes induced in the primary tumor. This study describes a novel method for studying the effects of hypoxia in solid tumors and demonstrates that acute and chronic hypoxia can have different effects on tumor cell behavior in vivo.

Animals↗
PubMed1999

Knee magnetic resonance imaging in childhood chronic monarthritis.

OBJECTIVE: To describe the usefulness of magnetic resonance imaging (MRI) of the knee in the evaluation of chronic monarthritis of uncertain cause in childhood. METHODS: We retrospectively reviewed 21 children referred to our clinic with a putative diagnosis of chronic inflammatory monarthritis of the knee who had MRI performed between May 1993 and June 1997. The median age was 13 years (range 2-17) and 11 were girls. RESULTS: The clinical diagnosis prior to MRI assessment was inflammatory arthritis in 16 patients, and a primary noninflammatory cause in 5. MRI was done in the patients with presumptive inflammatory arthritis when there were atypical symptoms, signs, or radiographs (n = 14), or when they failed to respond to therapy (n = 2). In the patients with a presumptive noninflammatory diagnosis, MRI was performed to clarify the diagnosis. Twelve children (57%) had MRI evidence of a noninflammatory diagnosis. In 4 children (19%) the MRI study indicated the presence of arthritis, and in 5 children (24%) the MRI studies were normal. The noninflammatory diagnoses included: lipoma arborescens (n = 1), vascular malformation [intraarticular (n = 1), extraarticular (n = 1)], synovial chondromatosis (n = 2), partial anterior cruciate ligament tear (n = 2), traumatic bone contusion (n = 2), possible meniscal tear (n = 1), osteochondritis dissecans (n = 1), and a soft tissue mass of uncertain significance in the suprapatellar pouch (n = 1). CONCLUSION: Inflammatory arthritis is usually diagnosed by clinical assessment alone. Uncommonly, when a single joint is involved, and atypical features are identified by a pediatric rheumatologist, other causes of chronic pain and swelling need to be excluded. In this selected patient population, MRI is a useful tool either to confirm the presence of inflammatory arthritis or to investigate a wide range of pathology that can mimic knee joint arthritis.

Adolescent↗
PubMed1996

Osteosarcoma in a 19-month-old girl.

Osteosarcoma develops only rarely in patients under 6 years of age. The authors describe a 19-month-old girl who presented with proximal humeral metaphyseal osteosarcoma. To the authors' knowledge, this report represents the youngest patient with this bone lesion.

Biopsy↗
PubMed1996

Congenital-infantile fibrosarcoma: magnetic resonance imaging findings.

Congenital-infantile, fibrosarcoma is a rare tumour presenting at birth or in the neonatal period. Few such tumours have been reported, and imaging details in particular are scant. The authors describe two neonates with congenital-infantile fibrosarcoma, the first case involving the right thigh and extending into the pelvis, and the second involving the calf and the ankle. In both cases magnetic resonance imaging (MRI) demonstrated well-demarcated, low-signal-intensity soft-tissue masses with t1-weighting and inhomogeneous, high-signal-intensity masses with T2-weighting. MRI was superior to other imaging modalities in the assessment of soft-tissue involvement and proved especially useful in planning therapy and monitoring chemotherapeutic response.

Biopsy↗
PubMed1995

Obstructive lung disease in children after allogeneic bone marrow transplantation: evaluation with high-resolution CT.

OBJECTIVE: Obstructive lung disease is a major complication of bone marrow transplantation related to graft-versus-host disease. The purpose of this study was to determine the usefulness of high-resolution CT to evaluate obstructive lung disease occurring in children after bone marrow transplantation. MATERIALS AND METHODS: Ten high-resolution CT scans of the lungs were obtained in seven children who developed chronic obstructive lung disease after bone marrow transplantation. All seven patients had chronic graft-versus-host disease. Spirometry, the gold standard test, confirmed airflow obstruction in each case, five prior to high-resolution CT. Two patients were too young to have spirometry until 10 and 15 months respectively after successful high-resolution CT. Selected images from these studies were randomized with similar images from five control subjects and reviewed blindly. All images from scans in patients with obstructive lung disease were analyzed retrospectively for parenchymal hypoattenuation, bronchial dilatation, bronchial wall thickening, and abnormal parenchymal opacity. Expiratory air-trapping was assessed on cine high-resolution CT done in four cases. RESULTS: Three blinded observers each correctly identified all five controls among 15 high-resolution CT examinations. No scan from a patient with obstructive lung disease was considered normal. Areas of parenchymal hypoattenuation affected 35 of 35 lobes of the lung. Expiratory air-trapping was shown by cine high-resolution CT. Subsegmental or segmental bronchial dilatation was seen in 23 of 25 lobes in five patients. Bronchial wall thickening was not a prominent feature. Increasing abnormality was demonstrated in three patients on follow-up high-resolution CT. The high-resolution CT abnormalities were similar to those reported in patients with bronchiolitis obliterans. CONCLUSION: High-resolution CT of the lungs can show extensive abnormality in children who develop chronic obstructive lung disease after bone marrow transplantation. High-resolution CT is a useful noninvasive technique in the evaluation of this disease.

Adolescent↗
PubMed1995

Atlantoaxial subluxation in children with seronegative enthesopathy and arthropathy syndrome: 2 case reports and a review of the literature.

We describe 2 HLA-B27 positive children with seronegative enthesopathy and arthropathy (SEA) syndrome who developed spontaneous (nontraumatic) atlantoaxial subluxation early in their disease course. Neither child had evidence of spinal cord compression but both had progressive atlantoaxial subluxation in spite of conservative treatment. Both underwent elective posterior cervical (C1-C2) fusion.

Adolescent↗
PubMed1994

Comparison of stimulable phosphor technology and conventional screen-film technology in pediatric scoliosis.

One hundred consecutive patients being investigated for scoliosis were studied using a double cassette containing a conventional film screen and a stimulable phosphor plate. The images were separated, randomised and scored thrice by three radiologists for anatomic structure visualisation. The exposure to the plate and film and repeat rate were measured. Scoliosis angles were comparable on both sets of images, however, visualisation of vertebrae, vertebral end plates, pedicles, spinous processes and other structures were significantly improved (p < 0.0001). Intra- and inter-observer reliability was high with good intraclass correlation. There was a 40% potential exposure reduction, and retakes were decreased from 3 to 0%. We conclude that stimulable phosphor images give better anatomic structure visualisation with potential radiation exposure reduction and lower repeat rate.

Child↗