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J Beck

Publications and source records attributed to J Beck.

At least 163 records · Page 9Linked to original sources
PubMed1993

Reciprocal modulation of the binding of angiotensin agonists and antagonists to angiotensin receptors in smooth muscle.

1. Direct ligand binding studies have shown that the agonist 125I-[Sar1]Ang II and the antagonist 125I-[Sar1Ile8]Ang II bind to bovine uterus smooth muscle membranes in a time-dependent, reversible and saturable manner; both ligands had the same number of high affinity sites. 2. [Sar1Ile8]Ang II inhibited the binding of 125I-[Sar1]Ang II in a non-competitive manner by decreasing the number of high affinity sites without changing the binding affinity of the radioligand. 3. [Sar1]Ang II also inhibited the binding of 125I-[Sar1Ile8]Ang II in a non-competitive manner. 4. Dissociation of both radioligands from their receptor sites was fast enough that pseudo irreversible occupancy of the binding sites could not account for the observed non-competitive inhibition. 5. Displacement studies using 125I-[Sar1Ile8]Ang II as the radioligand provided evidence for the existence of two binding sites when the displacing ligand was [Sar1]Ang II but not when the displacing ligand was [Sar1Ile8]Ang II. 6. GTPS gamma S had no discernible effect on the binding of either 125I-[Sar1]Ang II or 125I-[Sar1Ile8]Ang II to bovine uterine membranes. 7. The present findings are consistent with an allosteric mechanism of antagonism for [Sar1Ile8]Ang II. The data are also consistent with a mechanism wherein agonist and antagonist ligands occupy different binding modes at the same receptor site and induce long-term conformational changes in the receptor which are idiosyncratic with respect to the nature of the ligand. An emerging relationship between the actions of angiotensin peptides and non-peptide mimetics of angiotensin is presented.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1993

Work-related symptoms and checkstand configuration: an experimental study.

Supermarket checkers are known to be at risk of upper-extremity cumulative trauma disorders. Forty-two experienced checkers checked a standard "market basket" of items on an experimental checkstand. The counter height could be adjusted (high = 35.5, low = 31.5 inches), and the pre-scan queuing area length (between conveyor belt and laser scanner) could be set to "near" or "far" lengths. Each subject scanned under the high-near, high-far, low-near, and low-far conditions in random order. Seven ordinal symptom scales were used to describe comfort. Analysis showed that both counter height and queuing length had significant effects on symptoms. Furthermore, the height of the subject affected the degree and direction of the impact of the checkstand configuration differences. The study suggests that optimization of design may be experimentally evaluated, that modification of postural as well as frequency loading may be beneficial, and that adjustability for the individual may be advisable.

Adult↗
PubMed1993

Supermarket checker motions and cumulative trauma risk.

The relationship between specific motions and symptoms consistent with upper extremity cumulative trauma disorders (UECTDs) was investigated in 50 supermarket checkers. Each completed a questionnaire concerning UECTD symptoms; four composite symptom indices were derived: any arm symptoms, hand-wrist-lower arm (S-DIST), upper arm, and symptoms specifically associated with carpal tunnel syndrome (S-SPC). Each participant was videotaped on at least two occasions while performing checking work. Analysis of these tapes assigned each subject a composite motion index for each of the following motions: wrist flexion, wrist extension, body (lumbar) flexion, pronation, grip type, and tendency to lift objects. "Positive" symptom status was defined by a score in the upper quartile for the symptom index. Relationships between an individual's motion indices and symptom indices were analyzed by determining the percent of subjects "positive" for symptoms in each quartile of motion index, by rank correlation, and by regression of symptom scores on principal components of motions. Trends toward relationship of wrist flexion and extension, lumbar flexion, and pronation with S-DIST and S-SPC were noted. Principal components regression confirmed that extension and flexion were related to these two symptom outcomes. This study suggests that postural loading can be determined on an individual basis in a meaningful fashion and that interventions that decrease such loading may be beneficial. It supports the role of certain repetitive motions as causes of UECTD symptoms.

Adult↗
PubMed1993

Designing a connectionist network supercomputer.

This paper describes an effort at UC Berkeley and the International Computer Science Institute to develop a supercomputer for artificial neural network applications. Our perspective has been strongly influenced by earlier experiences with the construction and use of a simpler machine. In particular, we have observed Amdahl's Law in action in our designs and those of others. These observations inspire attention to many factors beyond fast multiply-accumulate arithmetic. We describe a number of these factors along with rough expressions for their influence and then give the applications targets, machine goals and the system architecture for the machine we are currently designing.

Algorithms↗
PubMed1993

Evidence against a proton pump in rabbit proximal convoluted tubule.

H+/OH- transport in the absence of bicarbonate was studied in the rabbit proximal convoluted tubule (PCT) perfused in vitro using measurements of membrane potential and intracellular pH (pHi). Blockade of apical Na/H exchange led to a cell acidification of 0.64 +/- 0.1 pH units from a control pHi of 7.27 +/- 0.04. A bafilomycin-insensitive recovery of pHi of 0.05 +/- 0.02 pH units occurred, but pHi did not exceed electrochemical equilibrium. A larger, sustained acidification of 0.87 +/- 0.07 from an initial control pHi of 7.25 +/- 0.05 induced by bilateral Na removal left pHi substantially below electrochemical equilibrium. These results suggest the absence of Na-independent active proton extrusion. We also examined the possibility that a passive electrogenic proton leak may exist. The removal of luminal glucose and alanine led to a basolateral membrane hyperpolarization of 31.3 +/- 0.5 mV, which was associated with a cell acidification of 0.15 +/- 0.02 pH units. These responses were reversed by addition of luminal glucose and alanine but not by depolarization by basolateral barium, suggesting that luminal glucose and alanine effects on pHi were due to changes other than cell potential. We conclude that, in the absence of bicarbonate, all active proton extrusion in the rabbit PCT is dependent on active Na transport and that a proton leak is negligible.

Animals↗
PubMed1993

The influence of vibrissae removal on copulatory behaviour in male rats.

The influence of vibrissae removal on copulatory behaviour was tested in both sexually naive and experienced male rats. The experiment consisted of 3 experimental and 3 control sessions. In some sexually naive rats, the removal of the vibrissae caused absence of copulatory behaviour during the first or all 3 experimental sessions, while in other ones this procedure remained without any apparent influence on copulatory behaviour. Three weeks later, after vibrissae have regrown, all of these rats displayed the copulatory behaviour. However, after the regrowth of the vibrissae, in rats with previously impaired copulatory behaviour a shortening of postejaculatory intervals was observed, while in rats with unaffected copulatory behaviour no such differences were observed. In contrast to observations in the sexually naive rats, in the sexually experienced ones removal of vibrissae led to the activation of copulatory behaviour, manifested by shortening of ejaculation latencies and mean interintromission intervals and an increase in hit rate.

Animals↗
PubMed1993

The role of sexual reward in the temporal patterning of copulatory behaviour in male rats.

In 8 male rats instrumental responses reinforced by contact with an estrous female with an intact or a surgically closed vagina were investigated. Contact with the female lasted until the end of the mount bout. It was observed that neither the rewarding value of the mount bout (expressed by the duration of the response) nor its arousing properties (expressed by the rate of bar presses) depended on the quality (mounts or intromissions) or quantity of the copulatory events of which it was composed. It is suggested that the temporal patterning of copulatory behaviour in male rats depends on fluctuations of sexual reward. This sexual reward can be a result of both genital stimulation as well as the performance of mounting under the influence of sign stimuli coming from the estrous female.

Animals↗
PubMed1992

Upper extremity symptoms in supermarket workers.

Upper extremity symptoms in supermarket workers, particularly those who performed checking using laser scanners, were evaluated using a questionnaire administered by trained interviewers to 124 supermarket workers. Summary indices of exposure (short-term and long-term) as well as indices of past personal illnesses and personal activities were employed. Outcome data were summarized by four composite symptom indices. Chi square and logistic regression analyses demonstrated that hours of checking work in the preceding 2 weeks and cumulative weighted years of work were associated with adverse upper extremity symptoms. Symptoms involved both the proximal and distal parts of the upper extremities.

Adult↗
PubMed1992

Nonlinear processes in spatial-frequency channel models of perceived texture segregation: effects of sign and amount of contrast.

Observers rated the degree of segregation between two textures, each composed of the same two element types but in differing arrangements (a checkerboard arrangement in the middle region of the pattern and a striped arrangement in the top and bottom regions). The two element types in a given pattern were either both solid squares or both center-surround elements. In center-surround elements the average luminance equaled the background luminance. The two elements types were identical in size but differed in sign and/or amount of contrast. Discrepancies between the observers' ratings of perceived segregation and the predictions of simple (linear) spatial-frequency and orientation channels models of texture segregation suggested adding nonlinear processes to the model. Complex channels (a rectification-type nonlinearity between two linear-filtering stages) can explain why some patterns made of center-surround elements segregate even though there is little energy at the spatial frequencies that differentiate the two textures. Complex channels cannot, however, explain the very poor segregation of "same-sign-of-contrast" patterns (where the luminances of the two element types were both far above or both far below the background). This second result might arise from a local nonlinearity preceding the channels and might be ascribed to retinal light adaptation except that it occurs at contrasts less than or equal to 25%! Alternatively, it might arise from normalization, which may result from intracortical inhibition. Some preliminary quantitative predictions were computed from two models, one incorporating complex channels and an early local nonlinearity, the other complex channels and normalization. With suitable choices of parameters, either model could account for the results.

Contrast Sensitivity↗
PubMed1992

Delayed c-fos expression in sensory cortex following sexual learning in male rats.

An elevated expression of c-fos protooncogene, encoding transcription factor Fos, is known to serve as a useful marker of neuronal activation. In the studies reported in this communication we have used Northern and dot blot techniques to analyze c-fos mRNA levels in male rat brain during the learning of the copulatory behavior. The animals were trained (single ejaculation in a training/testing session) for up to 7 sessions. C-fos mRNA levels have been found to increase in the sensory cortex area following the third and fifth session but not after the first and the last one.

Animals↗
PubMed1992

Follicular dynamics, plasma metabolites, hormones and insulin-like growth factor I (IGF-I) in lactating cows with positive or negative energy balance during the preovulatory period.

The effect of dietary energy balance (EB) on growth of ovarian follicles was tested. Cows (n = 9) were fed a high energy diet (HE diet; positive EB; n = 4) or switched to a low energy diet (LE diet; negative EB; n = 5) during the preovulatory period. Non-esterified fatty acids (NEFA) were greater in cows fed the LE diet. Concentrations of luteinizing hormone (LH) were similar in HE and LE cows. However, the growth of preovulatory follicles in cows fed the LE diet was 50% that of cows fed the HE diet. Insulin-like growth factor-I (IGF-I) in plasma was less in LE-fed cows compared with HE-fed cows, and plasma IGF-I was positively correlated to estrogen: progesterone ratio in follicular fluid of dominant follicles. In summary, slower follicular growth in cows fed an LE diet occurred despite normal plasma LH and coincided with reduced IGF-I and elevated NEFA in plasma.

Animals↗
PubMed1992

The differences between simultaneously or separately tested instrumental sexual responses in rats.

The instrumental sexual responses were investigated in male and female rats in the following experimental situations: (1) when the instrumental responses were tested simultaneously in the male and the female (2) when the male was a subject and the female was used as a reward only, and (3) when the opposite was true. The analysis of the data indicated that if the instrumental responses were tested separately in male and female rats, the male response latencies were significantly shorter than the female ones, while during the simultaneous testing no such difference was observed. This phenomenon seems to be a result of avoiding by the male rat of the frustration which occurs during waiting for the female after accomplishing the instrumental response.

Animals↗
PubMed1992

Luke May of Seattle--"America's Sherlock Holmes".

This paper provides a brief biography of Luke S. May (1886-1965), whose pioneering work in forensic science in the United States has not received full recognition. May began as a private detective in Salt Lake City, Utah, shortly after the turn of the century and later established his own agency, the Revelare International Secret Service, which he moved to Seattle, Washington, in 1919. Although basically self-taught in scientific matters, May built a solid reputation among police agencies and attorneys in the Pacific Northwest and Western Canada as a serious and effective scientific investigator in the era before public crime laboratories. This reputation as "America's Sherlock Holmes" also led to his being consulted on the establishment of the first American crime laboratory at Northwestern University in Chicago, Illinois, and on a laboratory for the Royal Canadian Mounted Police at Regina, in Saskatchewan, Canada. He contributed to a landmark case of court acceptance of toolmark identification, invented specialized instruments, and founded an institute to teach scientific criminal investigation to police officers. His earliest associates were John L. Harris and J. Clark Sellers, both of whom became recognized document examiners on the West Coast and were followed by a second and a third generation of practitioners.

Forensic Medicine↗