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Biomedical subjects

L J Cooper

Publications and source records attributed to L J Cooper.

At least 19 recordsLinked to original sources
PubMed2006

Efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser.

A novel approach to achieving robust single-spatial-mode operation of cladding-pumped fiber lasers with multimode cores is reported. The approach is based on the use of a fiber geometry in which the core has a helical trajectory within the inner cladding to suppress laser oscillation on higher-order modes. In a preliminary proof-of-principle study, efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser with a 30 microm diameter core and a numerical aperture of 0.087 has been demonstrated. The laser yielded 60.4 W of output at 1043 nm in a beam with M2 < 1.4 for 92.6 W launched pump power from a diode stack at 976 nm. The slope efficiency at pump powers well above threshold was approximately 84%, which compares favorably with the slope efficiencies achievable with conventional straight-core Yb-doped double-clad fiber lasers.

Journal Article↗
PubMed2005

High-power Yb-doped multicore ribbon fiber laser.

A highly elongated double-clad ribbon fiber that comprises a pure-silica inner cladding with transverse dimensions of approximately 1.4 mm by 0.23 mm with a linear array of ten ytterbium-doped cores has been fabricated and operated in a simple laser configuration pumped by two diode stacks. The fiber laser yielded 320 W of output power at a center wavelength of 1045 nm in a combined beam with beam propagation factors of approximately 2 (perpendicular to the array) and approximately 150 (parallel to the array) for 576 W of launched pump power. The slope efficiency with respect to absorbed pump power was 62%. The prospects for further power scaling and improved beam quality and efficiency are discussed.

Journal Article↗
PubMed2004

Efficient single-axial-mode operation of a Ho:YAG ring laser pumped by a Tm-doped silica fiber laser.

Efficient single-frequency operation of a Ho:YAG ring laser at room temperature with a traveling-wave TeO2 acousto-optic modulator to enforce unidirectional operation is reported. By use of a 2-at. % Ho3+-doped 10-mm-long Ho:YAG rod, end pumped by a cladding-pumped tunable Tm-doped silica fiber operating at 1.9 microm, the Ho:YAG ring laser yielded 3.7 W of single-frequency output at 2.1 microm in a diffraction-limited TEM00 beam with M2 < 1.1 for an incident pump power of 8.8 W. The rf power required for unidirectional operation was 0.3 W and corresponded to an increase in cavity loss for the lasing direction (due to diffraction) of only 0.5%. The prospects for further improvement in efficiency are discussed.

Journal Article↗
PubMed2000

Evidence that juvenile myelomonocytic leukemia can arise from a pluripotential stem cell.

Children with neurofibromatosis type 1 (NF1) carry germline mutations in one allele of the NF1 gene and are predisposed to myeloid malignancies, particularly juvenile myelomonocytic leukemia (JMML). Disruption of the remaining NF1 allele can be found in malignant cells. Flow cytometric cell sorting techniques to isolate the malignant cell populations and molecular genetic methods to assay for somatic loss of the normal NF1 allele were used to study an unusual child with NF1 and JMML who subsequently had T-cell lymphoma. The data show that malignant JMML and lymphoma cells share a common loss of genetic material involving the normal NF1 gene and approximately 50 Mb of flanking sequence, suggesting that the abnormal T-lymphoid and myeloid populations were derived from a common precursor cell. These data support the hypothesis that JMML can arise in a pluripotent hematopoietic cell.

Cell Differentiation↗
PubMed2000

Transfer of specificity for human immunodeficiency virus type 1 into primary human T lymphocytes by introduction of T-cell receptor genes.

The introduction of genes encoding T-cell receptor (TCR) chains specific for human immunodeficiency virus into T cells of infected patients represents a means to quantitatively and qualitatively improve immunity to the virus. Our results demonstrate that the high level of TCR expression required for physiologic functioning can be reproducibly achieved with retroviral vectors encoding full-length unmodified TCR chains under the control of a strong internal constitutive phosphoglycerate kinase promoter.

Cloning, Molecular↗
PubMed1999

Use of a concurrent operants paradigm to evaluate positive reinforcers during treatment of food refusal.

The authors evaluated the responsiveness of 4 preschool-aged children to positive reinforcers within a concurrent operants paradigm during mealtimes. The children were presented with two identical, concurrently available sets of food. Each set differed in quantity and quality of positive reinforcement paired with acceptance of each bite of food or in the number of bites of food required to obtain positive reinforcement. Experiment 1 evaluated 1 child's responsiveness to positive reinforcement while permitting escape from bite offers. Experiment 2 evaluated 2 children's responsiveness to positive reinforcement when escape extinction occurred. Results from these experiments suggested that the children were responsive to positive reinforcers and chose more often the bites paired with the greater quantity and/or quality of reinforcement. Experiment 3 evaluated 1 child's responsiveness to positive reinforcement both without and with escape extinction. Results suggested that positive reinforcement affected choice behavior and that escape extinction affected amount of food consumed.

Behavior Therapy↗
PubMed1999

Combining descriptive and experimental analyses of young children with behavior problems in preschool settings.

This investigation shows the merits of preceding experimental analyses with descriptive analyses of functional variables with preschool children who engage in problematic behavior. A two-phase descriptive analysis was conducted in daycare settings with three children. In Phase 1, the authors assessed the relation between child behavior and structural events. During Phase 2, the same behavior was replotted by functional variables. The results showed that when the descriptive data were plotted via functional variables, specific hypotheses could be generated regarding the variables controlling appropriate behavior. This procedure permitted the subsequent use of very brief experimental analyses to further identify functional relations. The use of descriptive analyses of functional rather than structural variables may be an important component in the assessment of problem behavior in community settings.

Behavior Therapy↗
PubMed1999

An analysis of choice making in the assessment of young children with severe behavior problems.

We examined how positive and negative reinforcement influenced time allocation, occurrence of problem behavior, and completion of parent instructions during a concurrent choice assessment with 2 preschool-aged children who displayed severe problem behavior in their homes. The children were given a series of concurrent choice options that varied availability of parent attention, access to preferred toys, and presentation of parent instructions. The results showed that both children consistently allocated their time to choice areas that included parent attention when no instructions were presented. When parent attention choice areas included the presentation of instructions, the children displayed differential patterns of behavior that appeared to be influenced by the presence or absence of preferred toys. The results extended previous applications of reinforcer assessment procedures by analyzing the relative influence of both positive and negative reinforcement within a concurrent-operants paradigm.

Attention↗
PubMed1998

Increasing compliance with medical procedures: application of the high-probability request procedure to a toddler.

The effects of high-probability (high-p) requests on compliance with low-probability (low-p) responses have received increased attention from applied investigators. This study examined the effects of a high-p procedure on a toddler's compliance with medical procedures. Compliance to low-p requests occurred more frequently following compliance to high-p requests, suggesting that this procedure may be useful across different topographies of compliance.

Behavior Therapy↗
PubMed1996

Choice-making treatment of young children's severe behavior problems.

The choice-making behavior of 5 young children with developmental disabilities who engaged in aberrant behavior was studied within a concurrent operants framework. Experimental analyses were conducted to identify reinforcers that maintained aberrant behavior, and functional communication training packages were implemented to teach the participants to gain reinforcement using mands. Next, a choice-making analysis, in which the participants chose one of two responses (either a mand or an alternative neutral response) to obtain different durations and qualities of reinforcement, was conducted. Finally, treatment packages involving choice making via manding were implemented to decrease inappropriate behavior and to increase mands. The results extended previous applications of choice making to severe behavior disorders and across behaviors maintained by positive and negative reinforcement.

Behavior Therapy↗
PubMed1996

Brief experimental analysis of stimulus prompts for accurate responding on academic tasks in an outpatient clinic.

Brief multielement designs were used to examine the effects of specific instructional strategies on accuracy of academic performance during outpatient evaluations of 4 children with learning disorders. Instructional strategies that improved accuracy on academic tasks were identified for all participants. These results suggest that the application of experimental analysis methodologies to instructional variables may facilitate the identification of stimulus prompts that are associated with enhanced academic performance.

Ambulatory Care Facilities↗
PubMed1996

The effects of meal schedule and quantity on problematic behavior.

We present 2 case examples that illustrate the effects of meal schedule and quantity on displays of problematic behavior. In the first example, self-injury displayed by a toddler with severe developmental delays was maintained by parent attention, but only when he was satiated for food. When he was food deprived, self-injury decreased but did not appear to be differentiated across low or high social conditions. In the second example, crying and self-injury displayed by an elementary-aged girl with severe disabilities were correlated: Both behaviors were associated with food quantity, and neither behavior was responsive to social stimuli. These results replicate and extend previous findings demonstrating that meal schedule or food quantity can affect problematic behavior. In the present studies, brief functional analyses of aberrant behavior provided useful information for interpreting distinct patterns of behavior displayed by each child. We discuss these results in terms of the concept of establishing operations.

Behavior Therapy↗
PubMed1995

Complementarity, specificity and the nature of epitopes and paratopes in multivalent interactions.

Structural elements of an antibody (Ab) or antigen (Ag) distant from the actual sites mediating contact between Ab and Ag can exert substantial influence on binding to, and discrimination among, multivalent targets. Consequently, multivalent molecules that express the same number of identical binding sites, but that differ in other structural features, can exhibit differences in their ability to discriminate between multivalent ligands. Here, Neil Greenspan and Laurence Cooper review evidence for these effects, and explore implications of the conclusion that effective specificity in multivalent interactions is not completely determined by the degree of complementarity between epitopes and paratopes.

Antigen-Antibody Reactions↗
PubMed1995

Use of component analyses to identify active variables in treatment packages for children with feeding disorders.

We evaluated the separate components in treatment packages for food refusal of 4 young children. First, treatment packages were implemented until food acceptance improved. Next, a component analysis was conducted within a multielement or reversal design to identify the active components that facilitated food acceptance. The results indicated that escape extinction was always identified as an active variable when assessed; however, other variables, including positive reinforcement and noncontingent play, were also identified as active variables for 2 of the children. The results suggest that the component analysis was useful for identifying variables that affected food acceptance.

Child, Preschool↗
PubMed1994

Variable domain-identical antibodies exhibit IgG subclass-related differences in affinity and kinetic constants as determined by surface plasmon resonance.

We have analysed the binding of variable domain-identical mouse monoclonal antibodies (mAb) of the IgG3, IgG1 and IgG2b subclasses, as well as F(ab')2 fragments derived from the IgG3 and IgG1 mAb, to a multivalent glycoprotein target. Using a biosensor device (BIAcore, Pharmacia Biosensor) that measures the mass of the antibody (or other receptor molecule) deposited on a sensor chip displaying the relevant epitopes, we found that the IgG3 mAb binds more effectively than the other antibody species at a high but not a low epitope density. The greater functional affinity associated with the IgG3 mAb, at high epitope density, was correlated with both slower dissociation rate constants and faster association rate constants in comparison with the IgG1 and IgG2b mAb and the F(ab')2 fragments derived from the IgG3 and IgG1 mAb. Evidence for slower dissociation kinetics for the IgG3 mAb versus the IgG1 and IgG2b mAb was also obtained by ELISA and flow cytometry. These results demonstrate that: (1) differences in heavy chain constant (CH) domains can significantly influence apparent functional affinity for multivalent antigen, as determined without the use of covalently modified primary or secondary antibodies; (2) differences in CH domains can alter both association and dissociation rate constants for interactions between IgG antibodies and multivalent antigen; and (3) these effects of CH domains depend on epitope density. The effect of constant region differences on the apparent association rate constants suggests new approaches for achieving better binding or functional effectiveness through antibody engineering.

Acetylglucosamine↗
PubMed1994

Brief hierarchical assessment of potential treatment components with children in an outpatient clinic.

Seven patients conducted assessments in an outpatient clinic using a prescribed hierarchy of antecedent and consequence treatment components for their children's problem behavior. Brief assessment of potential treatment components was conducted to identify variables that controlled the children's appropriate behavior. Experimental control via a brief reversal was achieved for 6 of the 7 children, (1 child continued to behave appropriately following initial improvement in behavior). For these 6 children, improved behavior occurred with changes in treatment components. Our results extend previous studies of direct assessment procedures conducted in outpatient clinic settings.

Ambulatory Care↗
PubMed1994

The impact of functional analysis methodology on outpatient clinic services.

The impact of the article by Iwata, Dorsey, Slifer, Bauman, and Richman (1982) on research in severe behavior disorders has been impressive. Equally impressive, however, but not as fully recognized, has been the impact of this methodology on the routine professional activities of those who employ functional analysis methods in their daily work. As one example of this impact, we describe the evolution of assessment procedures based on "brief functional analysis" methodology in our outpatient clinics. Less apparent have been the collateral effects that occur from using these procedures. Interactions with clients and colleagues have changed in ways that result in increased positive reinforcement. In this article, we briefly discuss the positive impact functional analysis has had on one specific work behavior--outpatient clinic assessment--and describe some of the generalized effects we have experienced in related aspects of our daily professional activities.

Ambulatory Care Facilities↗