Showing papers by "University of North Texas published in 1985"

Control and measurement of ultrashort pulse shapes (in amplitude and phase) with femtosecond accuracy

Abstract: The performances of a tunable femtosecond dye laser are analyzed using accurate correlation techniques. The source is a passively mode-locked dye laser, of which both the frequency and frequency modulation are controlled by one or two intracavity prisms. Interferometric second-order autocorrelations, with a peak-to-background ratio of 8 to 1, are used simultaneously with the conventional intensity autocorrelation and the pulse spectrum to determine the pulse shape. The main advantages of the interferometric autocorrelations are that they provide phase information otherwise not available, and they are more sensitive to the pulse shape than the intensity autocorrelation. The phase sensitivity is demonstrated in an analysis of the Gaussian pulses with a linear frequency modulation. Analytical expressions for the envelopes of the interferometric autocorrelations of typical pulse shapes are provided for quick pulse shape identification. A numerical method is used to analyze the more complex pulse shapes and chirps that can be produced by the laser. A series of examples demonstrates the control of this laser over various pulse shapes and frequency modulations. Pulse broadening or compression by propagation through glass is calculated for the pulse shapes determined from the fittings. Comparisons of autocorrelations and cross correlations calculated for the dispersed pulses, with the actual measurements, demonstrate the accuracy of the fitting procedure. The method of pulse shape determination demonstrated here requires a train of identical pulses. Indeed, it is shown that, for example, a train of unchirped pulses randomly distributed in frequency can have the same interferometric autocorrelation than a single chirped pulse. In the case of the present source, a comparison of the pulse spectrum, with that of the second harmonic, gives an additional proof that pulse-to-pulse fluctuations are negligible.

Two-Photon Absorption, Nonlinear Refraction and Optical Limiting in Semiconductors

Abstract: Two-photon absorption coefficients /32 of ten direct gap semiconductors with band-gap energy Eg varying between 1 .4 and 3.7 eV were measured using 1.06 µm and 0.53 um picosecond pulses. $2 was found to scale as E43, as predicted by theory for the samples measured. Extension of the empirical relationship between $2 and Eg to InSb with Eg = 0.2 eV also provides agree-ment between previously measured values and the predicted 02. In addition, the absolute values of $2 are in excellent agreement (the average difference being <26%) with recent theory, which includes the effects of nonparabolic bands. The nonlinear refraction induced in these materials was monitored and found to agree well with the assumption that the self-refraction originates from the two-photon-generated free carriers. The observed self-defocusing yields an effective nonlinear index as much as two orders of magnitude larger than CS2 for comparable irradiances. This self-defocusing, in conjunction with two-photon absorption, was used to construct a simple, effective optical limiter that has high transmission at low input irradiance and low transmission at high input irradiance. The device is the optical analog of a Zener diode.

Energy band-gap dependence of two-photon absorption

Abstract: We present measurements of the two-photon absorption coefficients /2 of 10 different semiconductors having band-gap energies between 1.4 and 3.7 eV. We find that 12 varies as Eg- 3 , as predicted by theory. In addition, the absolute values of 02 agree with theory, which includes the effect of nonparabolic bands, the average difference being less than 26%. This agreement permits confident predictions of two-photon absorption coefficients of other materials at other wavelengths. The ever-increasing role of semiconductors in lightwave technology has created a pressing demand for the characterization of the nonlinear-optical properties of these materials. Semiconductors are attractive as elements in nonlinear-optical devices because of their large and potentially extremely fast optical nonlinearities. A careful study of these macroscopic nonlinearities should allow one to determine the dependence of these nonlinearities on fundamental microscopic mechanical and electronic material properties (e.g., band gap, carrier lifetime, carrier effective mass). The data base formed by this information would then allow one not only to tabulate the materials that exhibit large nonlinearities but also to predict the specific material parameters that give rise to these high nonlinearities. This predictive capability is extremely important from the standpoint of searching for materials with large nonlinearities. A study of the nonlinear-optical properties of several semiconductors is presented here, and a relationship between the two-photon absorption coefficient (/32) and other material properties is verified. Ten different materials were experimentally studied for which the incident photon energy hw is less than the direct band-gap energy Eg but greater than Eg/2, so that two-photon absorption (2PA) is allowed.' Both 1.06and 0.53-jum picosecond pulses are used in transmission experiments, similar to those used previously by Bechtel and Smith, 2 on semiconductors with Eg ranging from 1.4 to 3.7 eV. We find that 02 is given by

Optical limiting in GaAs

Abstract: We have used two-photon absorption, self-defocusing, and optically-induced melting in GaAs to limit 1 μm picosecond pulsed radiation. The contribution to the limiting action from each of these mechanisms is discussed and demonstrated. Additionally, we measure a two-photon absorption coefficient of 26 cm/GW, which is in good agreement with the smallest values reported in the literature. A pulse-width study of the nonlinear absorption was conducted to isolate the effects of two-photon-generated free-carrier absorption. Results indicate that, even though the number of free-carriers is sufficient to severely defocus the incident beam, free-carrier absorption does not measurably contribute to the nonlinear absorption.

Loneliness and Relationally Competent Communication

Abstract: Loneliness is seen as a common social experience, best understood through the mechanisms whereby actors attribute causes for their loneliness. From an attributional perspective, the effects of loneliness chronicity on relational, or communicative, competence are delineated in three hypotheses and empirically tested among dyads involved in a conversational exercise. The hypotheses are generally supported, revealing that chronically lonely people generally do not perceive themselves or others as relationally competent and are perceived as incompetent by others as well.

The Demand for Irrigation Water in the High Plains of Texas, 1957–80

Abstract: A new method of calculating groundwater pumpage is used to estimate water demand. These results are used, via the Gisser-Sanchez model, to show that pumpage regulation is unlikely to be beneficial in the Texas High Plains. A sensitivity analysis is performed on present value profits under optimal control and competitive schemes, using different (water demand) slope and intercept values. The results indicate that the Gisser-Sanchez rule is useful in determining the divergence in pumpage time paths and percentage difference in profits, under the two schemes, but it is not insightful in determining the nominal difference in profits.

Special-Class Placement, Level of Intelligence, and the Self-Concepts of Gifted Children: A Social Comparison Perspective

Abstract: Two hypotheses derived from social comparison tested the influence of instructional segregation on the self-concepts of elementary school gifted children. The self-concept scores of half the children were assessed prior to their participation in a one-day-per-week segregated enrichment program for the gifted. The remaining children were tested during program participation. The higher self-concept scores of students assessed prior to the program were interpreted as support for the contention that the reduced heterogeneity of ability in gifted classrooms forces some gifted children to see their abilities in a less favorable light. Each group was further divided by high and low IQ scores (a misnomer). The lowest self-concept scores accrued to low IQ children assessed during program participation. This was interpreted as support for the notion that transition to segregated classes for the gifted most dramatically affects the self-concepts of those children who are at the low end of the distribution of abiliti...

A Semantic Field Approach to Passive Vocabulary Acquisition for Reading Comprehension.

Abstract: Traditionally, vocabulary study has been based on a word-by-word approach and, as such, has often been criticized as a component in ESL curricula. This study compares a traditional approach to vocabulary instruction with an approach based on the semantic fields of words that appeared in college-level reading texts. Half of the words presented to experimental groups (semantic field approach) were randomly selected and presented to control groups (traditional approach), according to the format used in current vocabulary texts. The semantic field approach was based on the association between five related words and a keyword that could be mentally substituted in context. Testing revealed some short-term advantage for the control groups, but no significant differences were revealed on long-term testing. Since experimental groups were exposed to twice as many words in the same amount of time, the findings lend support to the use of the semantic field approach. In addition, long-term testing revealed, for the words in this study, a highly significant difference favoring vocabulary taught experimentally over incidental learning that may occur during exposure to academic English.

Musical style preferences and aural discrimination skills of primary grade school children

Abstract: This study sought (a) to measure first-, second-, and third-grade students' preferential reactions to aurally presented musical stimuli representing various styles, (b) to determine the effects of ...

The Effects of Goal Proximity and Goal Specificity on Endurance Performance

Abstract: The purpose of the present investigation was twofold: to determine if subjects who set specific difficult goals perform significantly better than those who set "do your best" goals, and to examine the importance of goal proximity on the performance of the 3-minute sit-up test. Two experiments were conducted, and subjects (N = 96) in both were matched on ability and then randomly assigned to one of the following conditions: (a) short-term goals, (b) long-term goals, (c) short-term plus long-term goals, and (d) "do your best" goals. They were tested once a week for either 5 weeks (Experiment 1) or 3 weeks (Experiment 2). Subjects in the short-term goal condition had weekly sit-up goals, whereas those in the long-term goal condition had only an end goal Performance results from both experiments revealed no significant between-group difference. Questionnaire data indicated that all subjects tried hard, were committed to their goals, and were ego-involved. Manipulation checks revealed, however, that subjects f...

Perceived Risk as a Factor in Buying Foreign Clothes

Abstract: The notion of perceived risk as an influence on consumer behaviour and the influence of knowledge of country of origin on the decision process have been well documented. Little research, however, has investigated the nature of risk associated with foreign products. This study uses Bettman's concept of inherent/handled risk to isolate the risk attributable to specific countries and relates the risk to willingness to buy clothing from the countries and the importance of the country of origin in the decision process.

Oral Mucosal Lesions Among Elderly in Israel

Abstract: The prevalence of ulcerative or proliferative oral mucosal lesions (OML) is an important parameter in evaluating the oral health of an elderly population. This paper relates the prevalence of OML in an elderly population to possible risk factors and defined high-risk groups. The second objective was to examine whether effective prediction of OML was possible from interview data alone. The elderly population of a Jerusalem neighborhood was surveyed in 1981: 456 elderly were interviewed by trained interviewers, and their oral cavities were examined by an oral epidemiologist. Specific diagnoses were confirmed by an independent senior clinician. Almost 40% of the elderly presented ulcerative or proliferative oral mucosal lesions. The prevalence of these OML was strongly related to the condition and age of dentures. The association between these OML and oral hygiene disappeared after controlling for the condition of the denture. Two variables ascertained by interview--age of denture and self-reported suitability of denture--turned out to be strong predictors of denture condition.

Analysis of a mode-locked ring laser: chirped-solitary-pulse solutions

Abstract: We present measurements on mode-locked ring dye lasers that demonstrate the role of self-phase modulation in the saturable absorber dye. The resulting bandwidth increase plays an essential role in ultrashort pulse generation, because it leads to intracavity pulse compression in the presence of normally dispersive components. The role of various intracavity components (glass, coatings) in intracavity compression is analyzed. As opposed to extracavity compression, measurements of pulse amplitude and phase show that the nonlinear phase modulation can be completely compensated. The interaction of the light pulse with the absorber is analyzed using Maxwell–Bloch equations. Next, we find the steady-state solution for the problem of pulse propagation through an infinite periodic medium containing all the essential intracavity elements (bandwidth-limiting filter, amplifier, absorber, dispersive component). The condition that the solitary pulses be unchirped enables us to determine the optimum intracavity dispersion, which, in agreement with the experimental data, leads to the shortest pulses.

Development of a short form to assess perceived freedom in leisure.

Abstract: The paper describes the development of two versions of a short form to measure “perceived freedom in leisure.” These scales are based on Ellis and Witt's (1984) earlier development of five scales t...

Biofeedback-assisted relaxation: effects on phagocytic capacity.

Abstract: The purpose of this study was to investigate whether subjects who self-report high levels of stress have lower immunity, and whether “low”-immunity subjects under “high” stress could enhance phagocytic activity through biofeedback-assisted relaxation (BAR). During Phase 1, the level of stress and the level of phagocytic immune functioning (nitroblue tetrazolium test) were assessed as “high” or “low.” Significant chi-square analysis (x2=3.8624, df=1, p<.05) showed that subjects with “high” stress had “low” immunity. Sixteen “high”-stress, “low”-immunity subjects were randomly assigned to BAR and control groups during Phase 2. Following treatment, NBT changes showed significant increases (F=11.11, p<.003) for experimental group as compared to control group. White blood cell count and white blood cell differential were unchanged across blood samples for both groups. Experimental subjects reported significant decreases in tension-anxiety and increases in overall coping. BAR was concluded to have improved coping skills and phagocytic capacity. BAR affected the quality, rather than the quantity, of phagocytic neutrophils.

Cellular recovery of dividing and confluent C3H10T1/2 cells from N-methyl-N'-nitro-N-nitrosoguanidine in the presence of ADP-ribosylation inhibitors.

Abstract: The relationship between treatment with 3-methoxy-benzamide (MBA), a potent inhibitor of ADP-ribosylation reactions, and the response of C3H10T1/2 cells to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) has been examined. Quiescent cells effected potentially lethal damage repair (PLDR) over a 48-h period following MNNG and the repair was coincident with the removal of DNA strand breaks. MBA had no effect on PLDR but was very co-cytotoxic with MNNG in dividing cells. The presence of MBA caused the appearance of an additional number of DNA strand breaks following MNNG in both quiescent and dividing cells. These results suggest that ADP-ribosylation is required for normal cell cycle progression following DNA damage in dividing cells.

Self-defocusing in CdSe induced by charge carriers created by two-photon absorption.

Abstract: We observe self-defocusing of picosecond, 106-microm pulses in CdSe The effective nonlinear refraction can be 2 orders of magnitude larger than that of CS(2) We obtain good agreement with the theory presented here, which assumes that the self-refraction is caused by charge carriers created by two-photon absorption

Conversational skill and locus of perception

Abstract: The present study attempted to identify behavioral skills associated with global perceptions of communication competence and to determine if the relationship between competence and skills varies as a function of perceptual locus. Fifteen dyadic conversations were videotaped. Each interactant rated self and partner and was rated by four observers who viewed each tape. Results indicated that subjects' perceptions of their partners' skills accounted for 87% of the variance in subjects' ratings of partners' competence and 80% of the variance in subjects'self-perceived confirmation. Observers' ratings of subjects' skills predicted 83% of the variance in observers' ratings of subjects' competence. Observers'ratings of subjects'skills were unrelated to subjects' self-rated competence.

Temperature tolerance of nitrite-exposed channel catfish

Abstract: Upper temperature tolerances of channel catfish Ictalurus punctatus were determined with the critical thermal maximum (CTM) method after fish were exposed to various sublethal concentrations of nitrite for 24 hours at 20°C. The CTM was inversely related to nitrite concentration (r = -0.71; P < 0.01); group means ranged from 38.0°C for controls to 35.9°C for fish exposed to 1.4 mg NO2/L. As expected from previous studies, percent methemoglobin (a nonoxygen-carrying form of hemoglobin) was correlated with nitrite concentration (r = 0.85; P < 0.01), and thus was inversely correlated with CTM (r = -0.68; P < 0.01). These results indicate that nitrite-temperature interactions have the potential of adversely affecting the productivity of high-density channel catfish aquaculture systems, particularly those located in the southern U.S. during summer. Received June 5, 1984 Accepted November 28, 1984

Conflicts Between Ethics and Law in Counseling and Psychotherapy

Abstract: Codes of ethics are designed to guide and govern the behavior of the professional for whom they are written. In such fields as counseling, psychology, and social work, ethical standards are necessary to protect clients, guide professionals, safeguard the autonomy of professional workers, and enhance the status of the profession. Sometimes, however, the professional worker finds that the ethical standards of the profession seem to be in conflict with the law. These conflicts may arise in such areas as advertising, confidentiality, and clients' rights of access to their own files. The authors discuss the nature, ramifications, and implications of ethical-legal conflicts in the helping professions.

Unethical decisions: the impact of reinforcement contingencies and managerial philosophies

Abstract: Unethical behavior is a serious issue facing business organizations. This study reports the results of a laboratory experiment involving 338 subjects in an in-basket simulation requiring that they decide whether or not to give kickbacks. Subjects were divided into two groups—each assigned a different managerial philosophy. Subjects were rewarded for unethical decisions on the first three trials and punished for unethical decisions on the last three trials. Results on all six trials support the hypotheses that unethical decisions are dependent on reinforcement contingencies and partially (in the first three trials) support the hypothesis that unethical decisions are dependent on stated managerial philosophy.