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At least 793 records · Page 44Linked to original sources
PubMed2002

Plant responses to insect herbivory: the emerging molecular analysis.

Plants respond to herbivore attack with a bewildering array of responses, broadly categorized as direct and indirect defenses, and tolerance. Plant-herbivore interactions are played out on spatial scales that include the cellular responses, well-studied in plant-pathogen interactions, as well as responses that function at whole-plant and community levels. The plant's wound response plays a central role but is frequently altered by insect-specific elicitors, giving plants the potential to optimize their defenses. In this review, we emphasize studies that advance the molecular understanding of elicited direct and indirect defenses and include verifications with insect bioassays. Large-scale transcriptional changes accompany insect-induced resistance, which is organized into specific temporal and spatial patterns and points to the existence of herbivore-specific trans-activating elements orchestrating the responses. Such organizational elements could help elucidate the molecular control over the diversity of responses elicited by herbivore attack.

Animals↗
PubMed1979

A viscosity model of polyacrylamide gel electrophoresis.

In current theories of polyacrylamide gel electrophoresis, the idea prevails that molecular sieving relies on different accessibility of volume fractions and of cross-sectional area fractions (denoted "pores") to different-sized ions due to the effect of "geometric exclusion". This correlates with the assumption that all elements of a polyacrylamide network occupy fixed and unchangeable positions thus forcing colliding macro-ions to diffuse laterally in order to find an "accessible pore" and to resume motion in direction of the electrical field. However, the alternative conception would be equally well justified, i.e. the assumption that polyacrylamide chains represent smooth obstacles cleared aside under the electrokinetic pressure of a macro-ion. This explanation would even be preferable with respect to the molecular sieving effects occurring in solutions of "liquid polyacrylamide". Yet no theory exists as to describe such effects in quantitative terms. In the present article, a parameter is defined and discussed, which can be estimated by experiment, and which seems to be apt to characterize local resistivity of polymer structures against dislocation and deformation: the "fractional specific resistance". Definition of this parameter is based on the model of a "viscosity-emulsion" composed of two interpenetrating liquid compartments which are characterized by different levels of hydrodynamic friction and the spatial dimensions of which are inferred from Ogston's theory. This concept of "localized viscosity" may also serve as a link between theories of molecular sieving and of "macroscopic viscosity" of flexible polymers. The data of Morris, formerly taken as verifications of the "rigid-pore" concept, are now interpreted in terms of four factors responsible for sizediscrimination: collision frequency, duration of single contacts, size-dependent frictional force, and the extent of cooperation among fibres, due to crosslinking and to simultanous contacts of several fibres to a single macro-ion. Some functions relevant for problems of molecular weight determination by gel electrophoresis are discussed in relation to the suggested model.

Acrylamides↗
PubMed2002

Bloom syndrome and Fanconi's anemia: rate and ethnic origin of mutation carriers in Israel.

BACKGROUND: The Bloom syndrome gene, BLM, was mapped to 15q26.1 and its product was found to encode a RecQ DNA helicase. The Fanconi's anemia complementation group C gene was mapped to chromosome 9q22.3, but its product function is not sufficiently clear. Both are recessive disorders associated with an elevated predisposition to cancer due to genomic instability. A single predominant mutation of each disorder was reported in Ashkenazi Jews: 2281delATCTGAinsTAGATTC for Bloom syndrome (BLM-ASH) and IVS4 + 4AT for Fanconi's anemia complementation group C. OBJECTIVES: To provide additional verification of the mutation rate of BLM and FACC in unselected Ashkenazi and non-Ashkenazi populations analyzed at the Sheba Medical Center, and to trace the origin of each mutation. METHODS: We used polymerase chain reaction to identify mutations of the relevant genomic fragments, restriction analysis and gel electrophoresis. We then applied the Pronto kit to verify the results in 244 samples and there was an excellent match. RESULTS: A heterozygote frequency of 1:111 for BLM-ASH and 1:92 for FACC was detected in more than 4,000 participants, none of whom reported a family history of the disorders. The Pronto kit confirmed all heterozygotes. Neither of the mutations was detected in 950 anonymous non-Ashkenazi Jews. The distribution pattern of parental origin differed significantly between the two carrier groups, as well as between each one and the general population. CONCLUSIONS: These findings as well as the absence of the mutations in non-Ashkenazi Jews suggest that: a) the mutations originated in the Israelite population that was exiled from Palestine by the Roman Empire in 70 AD and settled in Europe (Ashkenazi), in contrast to those who remained; and b) the difference in origin distribution of the BS and FACC mutations can be explained by either a secondary migration of a subgroup with a subsequent genetic drift, or a separate geographic region of introduction for each mutation.

Bloom Syndrome↗
PubMedDate not supplied

[Anaesthesia. Resuscitation problems arising from the surgical treatment of chemodectomas in the carotid fork (author's transl)].

Chemodectomas in the carotid fork are rare and usually benign tumours. Their removal by surgery creates certain problems in terms of operating technique since they are, anatomically, awkwardly situated. An additional problem arises from loss of blood resulting from their removal and possible cardiac disturbance which might affect the functioning of the carotid sinus should the tumours have been situated in this region. Furthermore, the possible eventuality of having to clamp the internal carotid for a short or even long time, should the operation require it, presupposes a perfect knowledge of the patient's cerebral circulation. Hence, therefore, the necessity of a verification of this circulation by centrolateral carotid arteriography to confirm the permeability of the circle of Willis and a potentially good supply of blood when the blood in the region of the tumour is restricted. It is equally necessary to have a complete record of the general state of the patient's cardiovascular, circulatory, respiratory, renal and neurological conditions. These must, within certain limits, be deemed satisfactory before the decision to operate is taken. Indeed, it is these conditions that will determine the per-operative as well as the post-operative condition of the patient.

Adult↗
PubMed1992

Construction of a GT polymorphism map of human 9q.

To construct a framework map of human chromosome 9 consisting of highly informative markers, we identified 36 cosmid clones from chromosome 9 that contained long GT repeat sequences. The cosmids were found to cluster on the long arm of the chromosome, particularly in the q32-34 region. Thirteen highly informative polymorphisms from 9q were identified, with median observed heterozygosity 0.75 and median calculated heterozygosity based upon allele frequencies of 0.75. These new GT repeat polymorphisms (D9S56, D9S58-67), as well as anchor GT polymorphisms for D9S15 (MCT112, 9q13), and ABL and ASS (both 9q34.1) were utilized to construct a linkage map of human 9q by the typing of the Venezuelan Reference Pedigree. Care was taken to avoid errors, including analysis of the data with CHROMLOOK and verification of all double crossover events detected within a 30 cM interval by repetition of the marker analysis. The map was generated using the MAPMAKER program. All positions in the resulting map are favored by odds of greater than 10(4):1. The map has a sex-averaged length of 90 cM (Kosambi function) with a single maximum intermarker recombination fraction of 26%. All other intermarker recombination fractions are less than 15%. As D9S15 is known to be closely linked to markers on proximal 9p, and ASS/ABL are in band 34.1, this set of GT polymorphisms spans the length of 9q and provides a useful panel for linkage analysis of disease genes to this region. The marker order was confirmed by in situ hybridization of the cosmid clones to metaphase spreads of normal human chromosomes, which indicated an excess of recombination in the telomeric region in comparison to centromeric 9q, in agreement with previous chiasmata distribution observations. Two spontaneous new mutations for these GT repeat markers were identified, giving an overall observed spontaneous mutation rate of 0.00045 per locus per gamete. Direct observation of new mutations has not been previously reported for dinucleotide polymorphisms, but the observed rate is consistent with frequencies observed for other VNTR polymorphisms.

Base Sequence↗
PubMed2005

Efficient retrieval of vegetation leaf area index and canopy clumping factor from satellite data to support pollutant deposition assessments.

Canopy leaf area index (LAI) is an important structural parameter of the vegetation controlling pollutant uptake by terrestrial ecosystems. This paper presents a computationally efficient algorithm for retrieval of vegetation LAI and canopy clumping factor from satellite data using observed Simple Ratios (SR) of near-infrared to red reflectance. The method employs numerical inversion of a physics-based analytical canopy radiative transfer model that simulates the bi-directional reflectance distribution function (BRDF). The algorithm is independent of ecosystem type. The method is applied to 1-km resolution AVHRR satellite images to retrieve a geo-referenced data set of monthly LAI values for the conterminous USA. Satellite-based LAI estimates are compared against independent ground LAI measurements over a range of ecosystem types. Verification results suggest that the new algorithm represents a viable approach to LAI retrieval at continental scale, and can facilitate spatially explicit studies of regional pollutant deposition and trace gas exchange.

Algorithms↗
PubMed2003

Inducible expression system and marker-linked mutagenesis approach for functional genomics of Haemophilus influenzae.

Complete bacterial genomic DNA sequences have allowed application of genome-scale strategies to identify essential genes. Efficient generation of conditional loss of function mutations provides a means of characterization of this class of genes. Promoter systems conferring tight regulation are particularly applicable to generating such mutations and we sought to apply this approach for the analysis of an essential gene of Haemophilus influenzae. Therefore, we developed the use of a D-xylose-inducible promoter for verification of an essential role in growth for yraM, which encodes a putative periplasmic lipoprotein, in both H. influenzae Rd and virulent type b strains. This promoter was sufficiently tightly regulated to generate conditionally viable strains by inducible expression of YraM. A second approach was used to further characterize YraM. Natural transformation and an ordered mutant collection spanning the H. influenzae genome provide the means to target any gene of interest for mutagenesis and temperature-sensitive (TS) mutant isolation. This strategy was applied to generate a conditionally lethal allele of yraM. The resulting TS mutation was directly mapped to a single amino acid substitution within a motif conserved in all putative YraM orthologs and this mutation was shown to be sufficient to confer the TS phenotype.

Bacterial Proteins↗
PubMed2001

Pace-termination and pacing for prevention of atrial tachyarrhythmias: results from a multicenter study with an implantable device for atrial therapy.

INTRODUCTION: Patients with bradycardia requiring permanent pacing frequently suffer from additional atrial tachyarrhythmias (ATs). This study evaluated the safety and efficacy of atrial antitachycardia pacing (ATP) and the performance of pacing for AT prevention implemented into a new pacemaker. METHODS AND RESULTS: In patients with conventional indications for permanent pacing, an investigational DDDRP pacemaker (Medtronic AT500, model 7253) was implanted. The primary study objectives were to determine the safety of overall device functioning and its efficacy in terminating spontaneous AT. A secondary endpoint was to determine the reliability of AT detection. Pacemaker memory functions were used to analyze the impact of dedicated pacing algorithms on AT prevention. In 33 European and Canadian centers, 325 patients were enrolled (mean follow-up 2.3+/-1.3 months). Complication-free survival at 3 months was 88%. In 2,145 episodes stored with atrial electrograms, AT detection was confirmed in 97%. The algorithm for continuous overdrive pacing increased the percentage of atrial pacing to 97%. After ATP activation, 16,683 of 52,468 AT episodes were treated (120 patients). Of these, 8,903 episodes (53%) were terminated successfully by ATP. No proarrhythmic effect of preventive pacing or atrial ATP was observed. Preventive pacing algorithms increased the median percentage of atrial pacing from 62% to 97%. However, the number of AT/AF (atrial fibrillation) episodes (4.1 vs 4.1 per patient per day) and the time in AT/AF (13.7% vs 12.8%) was not significantly different before and after activation of preventive pacing. CONCLUSION: DDDRP pacing with a new system for AT therapy was safe and associated with successful pace-termination of AT in 53% of episodes. Preventive pacing and atrial ATP algorithms represent two new functions that can be implemented safely into pacemaker systems for nonpharmacologic treatment of ATs in patients requiring pacemaker therapy.

Adolescent↗
PubMed2005

Upscaling for the time-harmonic Maxwell equations with heterogeneous magnetic materials.

This paper presents a theoretical method for the upscaling of the time-harmonic Maxwell equations. We use the eddy current approximation of the Maxwell equations to describe the fields in heterogeneous materials. The magnetic permeability of the media is assumed to have random heterogeneities given by a Gaussian random field. The upscaling is based on the coarse graining method which applies projections and Green's function formalism in Fourier space to scale the electric field. An upscaled Maxwell equation is derived which includes an effective magnetic permeability tensor. The effective permeability explicitly depends on the given scale for the upscaling. The scale-dependent permeability is calculated by a second-order perturbative expansion, and we discuss the future verification and the application of the results.

Journal Article↗
PubMed1983

Quality assurance of selective culture media for bacteria, moulds and yeasts: an attempt at standardization at the international level.

To facilitate monitoring of culture media, a simple quantitative streaking technique, implying ever-decreasing numbers of colony-forming units per surface area, as in spiral plating, was developed. The procedure evaluates, in quantitative terms, the ability of media (1) to support the formation of colonies by organisms that it was designed to grow and (2) to resist colonization by organisms that it is expected to suppress. The procedure was therefore termed ecometric evaluation. The ecometric results appeared to agree well with observations made on productivity and selectivity of the media studied during routine examination of specimens. These encouraging results prompted further, rigorous standardization of ecometry. A template was developed to standardize inoculation and the depth of the agar was controlled to within +/- 10%. Finally the attributes of the inocula used were accurately defined. The standardized ecometric technique has been found useful for the following purposes: (1) to assess the practical significance of the inhibitory effect of gentamicin observed in some moulds and yeasts (this was solved by replacing poorer basal media by one particular richer modification, viz, yeast morphology agar); (2) the development of a blood-free selective enumeration medium for Campylobacter jejuni, i.e. sulphide iron motility agar plus the combination of antibiotics suggested by Skirrow (1977); and (3) verification of the absence of antimicrobial activity of enzyme preparations, e.g. catalase, used in culture media to remedy sublethal damage in certain groups of bacteria. Ecometric evaluation can now be recommended for (1) routine monitoring of consignments of dehydrated or ready-to-use, purchased media; and (2) in-house checking of the functioning of medium preparation departments. Only occasionally is it necessary to use conventional counting techniques to confirm the results.

Bacteria↗
PubMed2003

Feldkamp-based cone-beam reconstruction for gantry-tilted helical multislice CT.

Depending on the clinical application, it is frequently necessary to tilt the gantry of an x-ray CT system with respect to the patient and couch. For single-slice fan-beam systems, tilting the gantry introduces no errors or artifacts. Most current systems, however, are helical multislice systems with up to 16 slices. The multislice helical reconstruction algorithms used to create CT images must be modified to account for tilting of the gantry. If they are not, the quality of reconstructed images will be poor with the presence of significant artifacts, such as smearing and double-imaging of anatomical structures. Current CT systems employ three primary types of reconstruction algorithms: helical fan-beam approximation, advanced single-slice rebinning, and Feldkamp-based algorithms. This paper presents a generalized helical cone-beam Feldkamp-based algorithm that is valid for both tilted and nontilted orientations of the gantry. Unlike some of the other algorithms, generalization of the Feldkamp algorithm to include gantry tilt is simple and straightforward with no significant increase in computational complexity. The effect of gantry tilt for helical Feldkamp reconstruction is to introduce a lateral shift in the isocenter of the reconstructed slice of interest, which is a function of the tilt, couch speed, and view angle. The lateral shift is easily calculated and incorporated into the helical Feldkamp backprojection algorithm. A tilt-generalized helical Feldkamp algorithm has been developed and incorporated into Aquilion 16-slice CT (Toshiba, Japan) scanners. This paper describes modifications necessary for the tilt generalization and its verification.

Algorithms↗
PubMed1977

The use of hybrid cells in immunotherapy.

HARRIS et. al. isolated somatic hybrid cells (A9/SEWA) between polyoma-induced tumor and mouse fibroblast cell lines. Although these hybrid cells were no longer tumorigenic, we found that their immunogenicity was conserved. It therefore seemed to us that these antigenic, non transplantable, living cells would be an ideal tool for immunotherapy experiments. In our first experiments we assessed the immunoprotection afforded by A9/SEWA cells in both the SEWA tumor/A.SW mouse and C3HPy/C3H mouse systems. However, the efficiency of immunization with hybrid cells is dependent on the stability of the cells, especially in respect to the expression of the TATA. So we also tried to evaluate the immunogenicity as a function of the number of subcultures undergone by the hybrid line. In both systems, the immunogenicity was very good in the early subcultures but, in the C3HPy tumor/C3H mouse system, a loss of immunogenicity was observed as the number of subcultures increased. Thus any clinical application or immunization by hybrid cells would necessitate the verification of the presence of the tumor-associated antigens at each subculture. We are at present experimenting with various in vitro techniques for detection of the expression of these antigens.

Animals↗
PubMed2001

Linkage of the human inducible nitric oxide synthase gene to type 1 diabetes.

Exposure of human pancreatic islets to a mixture of cytokines induces expression of the inducible nitric oxide synthase (iNOS), impairs beta-cell function, and induces apoptosis. We performed a mutational scanning of all 27 exons of the human NOS2 gene and linkage transmission disequilibrium testing of identified NOS2 polymorphisms in a Danish nationwide type 1 diabetes mellitus (IDDM) family collection. Mutational screening was performed using PCR-amplified exons, followed by single stranded conformation polymorphism and verification of potential polymorphisms by sequencing. The transmission disequilibrium test was performed in an IDDM family material comprising 257 Danish families; 154 families were affected sibling pair families, and 103 families were simplex families. In total, 10 polymorphisms were identified in 8 exons, of which 4 were tested in the family material. A C/T single nucleotide polymorphism in exon 16 resulting in an amino acid substitution, Ser(608)Leu, showed linkage to IDDM in human leukocyte antigen DR3/4-positive affected offspring (P = 0.008; corrected P = 0.024). No other distorted transmission patterns were found for any other tested single nucleotide polymorphism or constructed haplotypes with the exception of those including data from exon 16. In conclusion, linkage of the human NOS2 gene to IDDM in a subset of patients supports a pathogenic role of nitric oxide in human IDDM.

Diabetes Mellitus, Type 1↗
PubMed1989

Motor hemiplegia and the cerebral organization of movement in man. II. The myth of the human extrapyramidal system.

Following a brief review of the concept of extrapyramidal system, clinical and anatomic evidence is presented against its relative prominence in man. It is proposed that the greatest part of those structures traditionally labeled as extrapyramidal effects its respective functional activities by way of the pyramidal tracts themselves. Such structures, centered around the basal nuclei, the cerebellum and possibly, the limbic areas of the prosencephalon are, according to the present suggestion, indeed, pre pyramidal. This model is based upon the clinical analysis of patients and agrees with more than one century of anatomic verifications in human brains, favoring the notion of the singularity of the human brain.

Extrapyramidal Tracts↗
PubMedDate not supplied

[Methodological obstacles encountered in the evaluation of psychotherapies of schizophrenic patients. A general review].

Through a critical review of literature, authors suggest a methodological reflexion about problems in evaluation of effects of psychotherapies of schizophrenics, taking into account not only individual techniques but also institutional ones with psychotherapeutic orientations. Among the main difficulties are: evaluation with too much unspecific and over simplified criteria, for example criterium of rehospitalisation; lack of real comparability between groups, or techniques, and lack of validity of randomisation, still considered as a pawn of methodological rigour; diversity of levels of experience, and education of therapists, too unmatched model of functional organisation of the different centers, and in the same time too unequal recruitment of patients and at length of proposed therapeutic programs. Moreover, and even before these methodological bias, a more basic obstacle must be considered. It is the non-opening of models to the falsification, denounced by Bignami as the impossible verification of the heuristic value of the proposed models, ie the impossible verification of the utility of the proposed programs for individual therapies of schizophrenics.

Bias↗
PubMed1999

Medication adherence in rheumatoid arthritis patients: older is wiser.

OBJECTIVES: To create a profile of individuals nonadherent to their medications in an age-stratified sample (ages 34-84) of community-dwelling rheumatoid arthritis patients. The relative contributions of age, cognitive function, disability, emotional state, lifestyle, and beliefs about illness to nonadherence were assessed. DESIGN: A direct observation approach was used in conjunction with structural equation modeling. All participants were administered a preliminary assessment battery. Medications were then transferred to vials with microelectronic caps that recorded medication events for all medications for the next 4 weeks. PARTICIPANTS AND SETTING: A volunteer sample of 121 community-dwelling rheumatoid arthritis (RA) patients were recruited from newspaper ads, posters, and via informal physician contact from private rheumatology practices in Atlanta and Athens, Georgia. Written verification of the RA diagnosis and a disease severity rating were obtained from personal physicians before patients were enrolled in the study. Patients were tested in a private physician's office, and their medication adherence was monitored electronically for a month in their every-day work and home settings. MEASUREMENTS AND RESULTS: Structural equation modeling techniques were used to develop a model of adherence behavior. Cognitive and psychosocial measures were used to construct latent variables to predict adherence errors. The model of medication adherence explained 39% of the variance in adherence errors. The model demonstrated that older adults made the fewest adherence errors, and middle-aged adults made the most. A busy lifestyle, age, and cognitive deficits predicted nonadherence, whereas coping with arthritis-related moods predicted adherence. Illness severity, medication load, and physical function did not predict adherence errors. Omission of medication accounted for nearly all errors. CONCLUSION: Despite strong evidence for normal, age-related cognitive decline in this sample, older adults had sufficient cognitive function to manage medications. A busy lifestyle and middle age were more determinant of who was at risk of nonadherence than beliefs about medication or illness. Thus, practicing physicians should not assume that older adults have insufficient cognitive resources to manage medications and that they will be the most likely to make adherence errors. Very busy middle-aged adults seem to be at the greatest risk of managing medications improperly.

Adaptation, Psychological↗
PubMedDate not supplied

An edge-element based finite element model of microwave heating in hyperthermia: method and verification.

Hyperthermia has been shown to improve local tumour control of superficial and deep seated lesions when combined with radiotherapy. There remains difficulty in heating larger tumours with conventional applicators, but this is being addressed by several new applicator designs. This paper presents a new numerical model of microwave heating which is designed to aid in the development of new applicators for superficial heating. The model is based on a finite element method which utilises vector valued basis functions instead of the more conventional scalar valued basis functions. These basis functions were chosen since they are inherently suited for the solution of Maxwell's equations due to their vector nature. The model was successfully verified against an analytic solution to the Mie scattering problem as well as against previously published measurements of heating from a modified water bolus attached to a conventional waveguide applicator. An accompanying paper describes an application of this model to the design optimization of this modified bolus.

Biophysical Phenomena↗
PubMed1995

Software safety in medical applications.

The use of software in safety-critical medical applications permits sophisticated functionality that would otherwise not be achievable. However, it is very difficult to ensure that software in these systems is dependable. In particular all software development techniques have limitations, and none can provide any guarantee of overall software dependability. Given this shortcoming, the approach that we have taken is to develop techniques that emphasize the verification of properties that are important to overall software dependability. In this paper we describe two techniques that support the implementation and verification of dependable software for an experimental neurosurgical device and safety-critical applications in general. The first technique involves the assurance of critical safety properties by a relatively simple software component known as a safety kernel. Situated between the application software and the application devices, the safety kernel enforces rules that govern the safe operation of the devices. The simplicity of the safety kernel facilitates its implementation and verification. In most cases, it is not possible to rely on testing to provide the necessary verification of the software in a safety-critical application. However, testing can play an appropriate and vital role in the demonstration of safety properties. The second technique takes this approach, utilizing automated testing and selected test cases to demonstrate useful system properties.

Neurosurgery↗