Responsivity optimization in magneto-optic sensors based on ferromagnetic materials.

In an effort to optimize magnetic field detection sensitivities, the Faraday responsivity vector, which determines the relationship between the Faraday rotation angle and an externally applied magnetic field, was investigated in magneto-optic sensors based on bismuth-doped iron-garnet films. Under externally applied fields, Faraday rotation is produced principally by domain rotation and domain wall motion, whose relative contributions depend on the domain geometry and the direction of laser propagation. When optically probed along a principal magnetization axis, Faraday rotation is driven by a single magnetization mechanism, and the responsivity is linearized (reduced to an effective Verdet constant). When the films are probed along an oblique angle to the principal axes, the relationship between the Faraday rotation and the external field becomes tensorial and much more complex. Although this may lead to more complicated phenomena, the interplay of domain rotation and domain wall bowing can be exploited to improve responsivity or bandwidth. A generalized model for the magnitude and direction of the responsivity vector is formulated, which gives predictions that are consistent with the experimental data. Applications to arrayed sensors and three-axis field measurements are discussed.

Time-dependent, three-dimensional simulation of free-electron-laser oscillators.

We describe a procedure for the simulation of free-electron-laser (FEL) oscillators. The simulation uses a combination of the MEDUSA simulation code for the FEL interaction and the OPC code to model the resonator. The simulations are compared with recent observations of the oscillator at the Thomas Jefferson National Accelerator Facility and are in substantial agreement with the experiment.

Experimental limit on optical-photon coupling to light neutral scalar bosons.

We report on the first results of a sensitive search for scalar coupling of photons to a light neutral boson in the mass range of approximately 1.0 meV (milli-electron volts) and coupling strength greater than 10(-6) GeV(-1) using optical photons. This was a photon regeneration experiment using the "light shining through a wall" technique in which laser light was passed through a strong magnetic field upstream of an optical beam dump; regenerated laser light was then searched for downstream of a second magnetic field region optically shielded from the former. Our results show no evidence for scalar coupling in this region of parameter space.

Single-element laser beam shaper for uniform flat-top profiles.

A novel design method is presented for a simple laser beam shaper. Unlike earlier reports and designs based on the 2-element model, we prove it is possible to convert a laser beam from a non-uniform profile to a uniform flat-top distribution with one single aspherical lens.

Second harmonic FEL oscillation.

We have produced and measured for the first time second harmonic oscillation in the infrared region by a free electron laser. Although such lasing is ideally forbidden, since the gain of a plane wave is zero on axis for an electron beam perfectly aligned with a wiggler, a transverse mode antisymmetry allows sufficient gain in this experiment for lasing to occur. We lased at pulse rates up to 74.85 MHz and could produce over 4.5 W average and 40 kW peak of IR power in a 40 nm FWHM bandwidth at 2925 nm. In agreement with predictions, the source preferentially lased in a TEM01 mode.

Sustained kilowatt lasing in a free-electron laser with same-cell energy recovery

Jefferson Laboratory's kW-level infrared free-electron laser utilizes a superconducting accelerator that recovers about 75% of the electron-beam power. In achieving first lasing, the accelerator operated "straight ahead" to deliver 38-MeV, 1.1-mA cw current for lasing near 5 &mgr;m. The waste beam was sent directly to a dump while producing stable operation at up to 311 W. Utilizing the recirculation loop to send the electron beam back to the linac for energy recovery, the machine has now recovered cw average currents up to 5 mA, and has lased cw with up to 1720 W output at 3.1 &mgr;m.

The relationship of residential instability to medical care utilization among poor mothers in New York City.

OBJECTIVES: This study examines the relationship between residential instability, including mobility and previous homelessness, and the use of medical care among previously sheltered and never-sheltered mothers in New York City. The study represents one of the first efforts to follow up on families after they are no longer homeless. METHODS: Mothers from 543 welfare families in New York City were interviewed, once in 1988 (Time 1) and again beginning in 1992 (Time 2). The sample included 251 families who first entered shelters after their 1988 interview, and 292 families who spent no time in shelters before or after that point. Mothers were asked about the source and volume of medical care used in the year before follow-up. RESULTS: Bivariate and multivariate analyses showed that previously sheltered mothers had a greater reliance on emergency departments (EDs) and weaker ties to private physicians or health maintenance organizations (HMOs) than did mothers who never used shelters. Mobility before the Time 1 interview was associated with greater reliance on EDs and absence of a usual source of care. More recent mobility was not associated with a usual source of care. Current residential stability reduced the likelihood of using an emergency department or having no regular source of care. None of the measures of residential instability were related to the volume of outpatient care used by mothers. CONCLUSIONS: A history of residential instability, particularly previous shelter use, strongly predicts where poor mothers currently seek health care. Further research is needed to determine whether these patterns of health care use existed before mothers entered shelters. The study provides evidence that upon leaving shelters, mothers are not being well integrated into primary care services.

Predictors of homelessness among families in New York City: from shelter request to housing stability.

OBJECTIVES: This study examined predictors of entry into shelter and subsequent housing stability for a cohort of families receiving public assistance in New York City. METHODS: Interviews were conducted with 266 families as they requested shelter and with a comparison sample of 298 families selected at random from the welfare caseload. Respondents were reinterviewed 5 years later. Families with prior history of shelter use were excluded from the follow-up study. RESULTS: Demographic characteristics and housing conditions were the most important risk factors for shelter entry; enduring poverty and disruptive social experiences also contributed. Five years later, four fifths of sheltered families had their own apartment. Receipt of subsidized housing was the primary predictor of housing stability among formerly homeless families (odds ratio [OR] = 20.6, 95% confidence interval [CI] = 9.9, 42.9). CONCLUSIONS: Housing subsidies are critical to ending homelessness among families.

In vivo role of glucocorticoids in barotrauma vascular repair and fibrosis.

To determine the important repair events leading to vascular collagen accumulation following barotrauma, in vivo changes were assessed during dexamethasone (DEX) treatment, as well as physiological healing. Hypercholesterolemic rabbits underwent bilateral iliac artery endothelial denudation, followed by angioplasty. Messenger ribonucleic acid (RNA) (procollagen types I, III and transforming growth factor [TGF]beta1), and bio-histometric composition of iliac arteries of animals treated with DEX (2, 7 and 7 days; 1 mg/kg1/day1), were compared to that in controls 2, 7 and 30 days after angioplasty. Type I and III procollagen mRNA transcripts were up-regulated following injury in either group. Similarly, TGFbeta1 mRNA levels were also elevated; however, treatment with DEX led to down-regulation at day 30 post-angioplasty. Linear regression and correlation of the densitometric ratios of procollagen alpha1(I) and TGFbeta1 mRNA during repair were observed significantly in either group (DEX-treated, r2= 0.84; non-treated, r2=0.79). Biochemically derived total vascular RNA concentration decreased transiently (7 days), with DEX-treatment (P = 0.003). Arterial lumen cross-sectional area was reduced between days 2 and 30 (P=<0.02), accompanied by an increase in fibrillar collagen concentration in both groups of animals post-angioplasty. These results suggest that during barotrauma repair, administration of DEX (approximately 1 week), does not affect vascular intimal hyperplasia or fibrosis, and that despite treatment, significant production of type I procollagen mRNA continues, influencing subsequent collagen deposition. The data also confirm a strong correlation between TGFbeta1 and type I procollagen mRNA expression, and modestly with type III procollagen during post-angioplasty repair.

Family homelessness: state or trait?

Compares conceptualizations of homelessness as a temporary state through which people pass or a permanent trait that emanates from individual characteristics. Evidence from a longitudinal study of 564 homeless families in New York City and additional secondary sources supports the view that for families, homelessness is a temporary state that is resolved by the provision of subsidized housing. Even for single individuals with severe mental disturbances, housing is a key factor in ending homelessness, although here there is more evidence that social services also contribute. Policy implications are that governments should take a more active role in reducing homelessness by providing access to subsidized housing.

The utility of curriculum-based measurement for evaluating the effects of methylphenidate on academic performance.

Two case studies were conducted to investigate the utility of curriculum-based measurement of math and reading for evaluating the effects of methylphenidate on the academic performance of 2 students diagnosed with attention deficit hyperactivity disorder. Following baseline measurement, double-blind placebo-controlled procedures were employed to evaluate each student's response to three levels (5 mg, 10 mg, and 15 mg) of the medication. Results of the first study suggest that the curriculum-based measures were sensitive indicators of the student's response to medication. This finding was replicated in the second study. In the second study, when the student's follow-up dose of medication was based on trial-phase data, follow-up performance was improved compared to baseline performance. These case studies suggest that further research is warranted on the utility of curriculum-based measurements for monitoring and evaluating stimulant medication interventions with children with this disorder.

Predictors of shelter use among low-income families: psychiatric history, substance abuse, and victimization.

For poor housed and homeless families in New York City, NY, we examined the degree to which psychiatric and substance-abuse problems and victimization placed the families at elevated risk of requiring emergency housing, and we documented the prevalence of such problems. These problems were infrequently reported by both groups. However, past mental hospitalization, treatment in a detoxification center, childhood sexual abuse, and adult physical abuse were associated with increased risk of homelessness.

Homelessness: what is a psychologist to do?

Contrasts person-centered and structural explanations for homelessness. Methodological problems in studies of homeless people tend to exaggerate the role of individual deficits as causes of homelessness. A review of data on the distribution of poverty and of inadequate and unaffordable housing, with special emphasis on families, suggests the importance of structural causes. Data from 700 families requesting shelter and 524 families randomly drawn from the public assistance case load in New York City provide more support for a structural than for an individual deficit model. Individual demographic factors are also important. Implications are drawn for research and action by psychologists.

The impact of homelessness on children.

This article reviews and critiques community-based research on the effects of homelessness on children. Homeless children confront serious threats to their ability to succeed and their future well-being. Of particular concern are health problems, hunger, poor nutrition, developmental delays, anxiety, depression, behavioral problems, and educational underachievement. Factors that may mediate the observed outcomes include inadequate shelter conditions, instability in residences and shelters, inadequate services, and barriers to accessing services that are available. Public policy initiatives are needed to meet the needs of homeless children.

Social relationships and vulnerability to becoming homeless among poor families.

This study compares social relationships of 677 mothers in families requesting shelter with those of 495 mothers in housed families, randomly selected from the public assistance caseload in New York City. As hypothesized, women seeking shelter had experienced higher levels of a variety of childhood and adult events indicative of disruptions in social relationships. Contrary to our hypothesis, they were more likely than were housed mothers to have had recent contact with parents, other relatives, and friends, although they felt less able to draw on these resources for help with their current housing needs. More than three fourths of families seeking shelter had already stayed with members of their social network in the past year. The data suggest that they had used up potential sources of support before turning to public shelter.

Continuous EGF application impairs long-term collagen accumulation during wound healing in rats.

Continuous topical application of epidermal growth factor (EGF) to granulation tissue has been demonstrated to increase the rate of collagen accumulation in wounds. Studies from this laboratory have indicated that a single topical application of EGF leads to a short period of elevated wound collagen content, followed by a rapid breakdown of this newly acquired collagen. In light of recent clinical trials of EGF as an aid to wound healing, we studied the long-term effects of continuous EGF injection. Standard polytetrafluoroethylene (PTFE) wound cylinders were surgically placed in the dorsal midline of 40 male Sprague-Dawley rats. Rats received EGF daily for 14 days, at which time all injections ceased. Wound cylinders were removed for analysis from five test animals and five controls on study days 14, 21, 28, and 35. Wound collagen content in EGF-treated animals was significantly higher than in controls on the 14th day of the study (330% higher, P less than .002), but dropped to lower levels on each succeeding day (day 21: 97% of control, NS; day 28: 63% of control, NS; day 35: 72% of control, P less than .03). There was a significant increase in wound collagenase activity only on days 14 and 21, but not on days 28 and 35. We demonstrated that continuous application of EGF may artificially elevate wound collagen content, thereby leading to increased wound catabolism on cessation of treatment.

Crossing substantive domains.

This paper advocates a middle ground between detailed immersion in a single context and broad generalizations that ignore context. Contextual constraints are best understood when context is varied explicitly. For example, both the content and the effects of coping efforts and social support varied with context across several studies. Comparison across substantive domains is an important tool for understanding both theory and any specific domain.

Stimulated-emission cross sections of the (5)F(1)-(5)I(5) and (5)F(1)-(5)I(6) transitions of Pm(3+) in a phosphate glass.

We report a laser cavity measurement of stimulated-emission cross sections for both the (5)F(1)-(5)I(5) (0.93-microm) and (5)F(1)-(5)I(6) (1.1-microm) laser transitions of Pm(3+) ions in a lead-indium-phosphate glass host. The measured cross sections for these two transitions are 1.8 x 10(-20) (+/-11%) and 2.8 x 10(-20) cm(2) (+/-22%), respectively. These values agree with previously reported values based on a Judd-Ofelt-type analysis of spectroscopic data.