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Biomedical subjects

P Rees

Publications and source records attributed to P Rees.

At least 19 recordsLinked to original sources
PubMed2003

Nullified time-of-flight lead-lag in synchronization of chaotic external-cavity laser diodes.

Synchronization of three chaotic diode lasers is effected in a transmitter-mediator-receiver configuration. The transmitter laser's output is bidirectionally coupled to the mediator laser to achieve anticipating synchronization in their output intensities. The mediator laser's output is unidirectionally coupled to the receiver laser to achieve lag synchronization in their output intensities. This combination of lead and lag synchronization nullifies the time-of-flight lead-lag in synchronization between the transmitter and receiver lasers. This approach provides a means of eliminating time-of-flight delays in the synchronization of remote transmitters and receivers.

Journal Article↗
PubMed2000

Genetic characterization of strain differences in the ability to mediate CD40/CD28-independent rejection of skin allografts.

Simultaneous blockade of the CD40 and CD28 T cell costimulatory pathways effectively promotes skin allograft survival in C3H/HeJ mice, extending median survival times (MSTs) beyond 100 days. This strategy is markedly less effective in C57BL/6 mice, with MSTs ranging between 20 and 30 days. In this study, we investigate the underlying genetic causes of these distinct phenotypes. Using H-2 congenic mice, we show that the genetic basis for the varied responses between these two strains is independent of the H-2 locus and T cell precursor frequency. C57BL/6 mice treated with costimulation blockade are able to generate allospecific CTL- and IFN-gamma-producing T cells within 3-4 wk posttransplant, whereas mice with a C3H background generate neither CTL- nor IFN-gamma-producing cells. Thus, differences appear to be in the generation of the immune response and not T cell homing. Strain differences in costimulation blockade-induced hyporesponsiveness persist in the absence of CD4(+) T cells, implying a direct effect on CD8(+) T cells. We demonstrate that genetic differences are important in cells of hemopoietic origin and that the costimulation blockade-resistant phenotype is dominant. Analysis of BXH recombinant inbred strains indicates that multiple loci contribute to the phenotype, and that the blockade resistance loci are preliminarily linked to 17 markers on four chromosomes. We conclude that strain variation in allograft MSTs following CD40/CD28 blockade results from the ability of CD8(+) T cells in some strains to use alternative modes of costimulation to mount an effective alloresponse.

Abatacept↗
PubMed2000

Cardiac malformations associated with the congenital nephrotic syndrome.

The association of cardiac malformation with the congenital nephrotic syndrome (CNS) has been previously reported in only one family. We report four patients with CNS: three with pulmonary valve stenosis (one requiring valvuloplasty) and one with discrete subaortic stenosis requiring surgical resection. We conclude that the cardiac status of all patients with CNS should be reviewed regularly by a paediatrician, with a low threshold for referral to a cardiologist, as flow murmurs due to chronic anaemia may obscure cardiac pathology. It is important to diagnose any associated cardiac lesions as these may require intervention, and may also predispose to the development of bacterial endocarditis if surgical or dental procedures are undertaken without appropriate antibiotic prophylaxis.

Aortic Valve Stenosis↗
PubMed2000

Wavelet operators for nonlinear optical pulse propagation.

A method that uses discrete wavelet transforms for the solution of evolution equations that describe optical pulse propagation in nonlinear media is presented. The theory of orthogonal wavelet transforms is outlined and applied to the representation of optical pulses. Wavelet transform representations of propagation operators are presented and applied to the nonlinear Schrödinger equation, yielding results that are indistinguishable from traditional Fourier-based simulations. The compression properties of wavelet representations of optical pulses permit significant improvement in execution speed compared with that of the split-step Fourier method.

Journal Article↗
PubMed1999

Heart or heart-lung transplantation: psychosocial outcome.

The psychosocial outcome of 23 heart and 21 heart-lung transplant recipients, aged 5-17 yrs, was determined and compared with the psychosocial outcome of a group of 46 children and adolescents who underwent conventional cardiac surgery. Preoperatively, and 12 months post-operatively, the patients' physical health status, mental state (ICD-9) and level of psychosocial functioning (GAF scale, DSM-IIIR) were assessed. There was an improvement in physical health in all groups. Preoperatively, psychiatric disorder, including anxiety and phobic states, depression and adjustment reaction, was noted in 6/23 (26%) children assessed for heart transplantation, 6/21 (28.5%) children assessed for heart-lung transplantation, and 12/46 (26%) children undergoing conventional cardiac surgery. The prevalence of psychiatric disorder remained in the transplant group but decreased in the non-transplant comparison group (6.5%). Improvement in overall levels of psychosocial functioning were found in all groups, but over 40% of all the participants were still functioning below normal levels. In summary, children with end-stage cardio-respiratory disease benefit physically and psychologically from heart or heart-lung transplantation treatment but there is a need for systematic psychosocial support both before and after transplantation.

Adolescent↗
PubMed1999

Linking 1991 population statistics to the 1998 local government geography of Great Britain.

This article describes how 1991 population statistics and other data based on the 1991 Census areas can be produced for the 1998 local authority geography of Great Britain. Since 1991 a large number of boundary changes have taken place rendering comparisons of population data before and after the changes problematic. Re-basing 1991 statistics on the current set of boundaries allows real demographic change over the period since 1991 to be measured. The article focuses on two sets of population statistics: 1991 Census data and mid-1991 estimates.

Adolescent↗
PubMed1998

Can census offices publish statistics for more than one small area geography? An analysis of the differencing problem in statistical disclosure.

"The paper describes a problem faced by National Statistical Offices when publishing the results of decennial censuses for small geographical areas. If they publish statistical tables for two or more sets of areas, users can compare the tables and produce new statistics for the areas formed by differencing, which may have populations below confidentiality thresholds. To investigate the problem, the authors construct a software system and carry out a series of experiments using a large synthetic population base for Yorkshire and Humberside [in England]. The results indicate that publishing statistics for zones close in size to the primary areas is not safe unless the zones have been carefully designed. However, publishing statistics for sufficiently large areas such as 5km grid squares or postal sectors alongside enumeration districts is safe."

Censuses↗
PubMed1997

The selection of internal migration models for European regions.

"A full multiregional projection model requires migration data that are simultaneously classified by age and gender and region of origin and region of destination. Except for a very small number of regions, these data requirements are so high that aggregation of the data (which is equivalent to simplification of the model) is called for. This paper investigates the extent to which the full internal migration matrix can be simplified without seriously affecting the performance of the resulting multiregional model. Using IPF (iterative proportional fitting) methods, a log-linear analysis of alternative model specifications is made, using data for Italy, the Netherlands and the UK....A reasonable balance between goodness-of-fit and parsimony is found for the model in which time interacts with the main effects only (i.e. with age/sex, with origin and with destination)."

Age Factors↗
PubMed1997

Problems and solutions in forecasting geographical populations.

"This paper asks the question: How does the multistate population model need to be adjusted to provide forecasts of geographical populations? Following an exposition of the standard model, possible solutions to the problems posed by excessive number of parameters are discussed. Decomposition, aggregation and parameterization are described, drawing on some new results. Issues in the temporal forecasting of model components are outlined and the alternative approach of using a spatial interaction model is considered. The paper concludes by arguing that the design of forecasting models is a powerful learning device for both designers and users."

Forecasting↗
PubMed1996

Placenta increta occurring in a blighted ovum.

We present a rare case of placenta increta, confirmed postoperatively by pathologic analysis, occurring before 20 weeks' gestation in a blighted ovum. Hysterectomy was necessary for control of hemorrhage.

Adult↗
PubMed1996

Effects of heat shock on gram negative bacteria: use of lysis by sodium dodecyl sulphate as a probe for the integrity of DNA.

Rheograms of Alcaligenes eutrophus (NCIMB 40529) and Escherichia coli (C90 NCIMB 10616) cells lysed by sodium dodecyl sulphate were compared before and after a variety of heat shock regimes. It was found that unheated cells produced a very characteristic shear thickening rheogram which could be destroyed by DNase treatment. Cells which had been subjected to heat shock produced rheograms very similar to DNase digested material. We thus suggest that the rheogram is largely due to the presence of intact DNA molecules. The extent and nature of the heat shock affected the shape of the rheogram of the SDS lysed material. Heat shock of cells after SDS lysis did not appear to significantly damage the DNA. Storage of the cells at 10 degrees C before heat shock considerably reduced the shear thinning effect of subsequent heat shock at 90 degrees C. We attribute the shear thinning effect of the heat shock to the action of nucleases which are activated and then depolymerise the DNA molecules.

Alcaligenes↗
PubMed1995

Indexing the census: a by-product of the simulation of whole populations by means of SAS and SAR data.

"Amongst the new output formats adopted for the 1991 [U.K.] census were the Small Area and Local Base Statistics tables and the Samples of Anonymised Records. During an attempt to combine these data sources to estimate whole populations, a need was recognised for a computer algorithm to aggregate SAR data flexibly into LBS and SAS table look-alikes. This paper is a report on progress in the development of such an algorithm, including the concomitant development of a meta-database of census tables and variables required as an input to the algorithm. Out of this work a user-friendly, freely disseminable version of the census meta-database has been created, of interest to all census users."

Censuses↗