Biomedical subjects

T Meijer

Publications and source records attributed to T Meijer.

4 recordsLinked to original sources

PubMed2006

Blue five-level frequency-upconversion system in rubidium.

We demonstrate production of continuous coherent blue laser light by using a five-level system in rubidium vapor. Two low-power lasers, at 780 and 776 nm, induce strong atomic coherence in the 5S-5P-5D states. The atoms decay to the 6P excited state, from which stimulated emission produces a coherent blue (420 nm) beam. We have coupled both ground-state hyperfine levels, effecting coherence between four levels. The coherent blue output is enhanced by several mechanisms, including stronger coupling to a larger fraction of the atomic population, operation at a detuning such that the vapor is nominally transparent to the 780 nm pump field, reduced losses owing to optical pumping, and optimal phase matching. We report experimental findings and compare them with results from a semiclassical Maxwell-Bloch model.

Journal Article↗

PubMed2001

Different effort constructs and effort-reward imbalance: effects on employee well-being in ancillary health care workers.

AIMS OF THE STUDY: The present study investigates the relationship between Effort-Reward Imbalance (ERI) and employee well-being, using three different concepts of efforts (i.e. psychological demands, physical demands and emotional demands). BACKGROUND: The ERI model had been used as a theoretical framework, indicating that work stress is related to high efforts (i.e. job demands) and low occupational rewards (e.g. money, esteem and security/career opportunities). The ERI model also predicts that, in overcommitted workers, effects of ERI on employee well-being are stronger compared with their less committed counterparts. METHODS: A cross-sectional survey among 167 ancillary health care workers of two nursing homes was conducted. Multiple univariate logistic regression analyses were used to test the relationship between ERI and employee well-being. RESULTS: Results of the logistic regression analyses showed that employees with both high (psychological, physical and emotional) efforts and low rewards had higher risks of psychosomatic health complaints, physical health symptoms and job dissatisfaction (odds ratios (ORs) ranged from 5.09 to 18.55). Moreover, employees who reported both high efforts and high rewards had elevated risks of physical symptoms and exhaustion (ORs ranged from 6.17 to 9.39). No support was found for the hypothesis on the moderating effect of overcommitment. CONCLUSION: Results show some support for the ERI model; ancillary health care workers with high effort/low reward imbalance had elevated risks of poor employee well-being. In addition, results show that the combination of high efforts and high rewards is important for employee well-being. Finally, some practical implications are discussed to combat work stress in health care work.

Adolescent↗

PubMed1989

Hormonal patterns in breeding and nonbreeding kestrels, Falco tinnunculus: field and laboratory studies.

Plasma levels of luteinizing hormone (LH), androgens, and corticosterone (B) were measured in breeding and nonbreeding kestrels, both in the field and in captivity under different food conditions. LH levels in breeding males were elevated from courtship through incubation and androgen concentration peaked during courtship and laying. Seasonal changes in LH and androgens were similar in breeding and nonbreeding males, although androgens declined sharply after laying in breeding males. Egg laying was characterized by marked increases in both female body mass and plasma concentrations of LH and B. In both breeding and nonbreeding females LH and B increased during pair formation and courtship (March-April), although maximum levels were lower in nonbreeders. Two marked differences were found between free-living and captive (paired) birds. First, during winter plasma levels of LH were basal in free-living birds, while significantly elevated in both captive males and females. Second, during courtship androgen levels in breeding males were three-fold higher in the field than in captivity, probably as a result of intermale aggression under natural conditions. Females breeding early, late, or not at all had similar LH concentrations on arrival and during early courtship. Before breeding there were also no differences in LH (males and females) or in androgen levels (males) between pairs fed ad libitum and pairs temporary food rationed. However, captive females with experimentally reduced food intake showed low levels of B until their rations were increased. Nonbreeders showed hormonal changes similar to breeders, except for those changes in females that were associated with laying. These results suggest that at the start of the breeding season both nonbreeding and breeding kestrels have functional reproductive systems. That some breed early, late, or not at all is primarily an effect of food availability and is not due to hormonal modulation of the reproductive cycle.

Androgens↗

PubMed1989

Photoperiodic control of reproduction and molt in the kestrel, Falco tinnunculus.

An adaptive decline in average clutch size with progressive date of laying is characteristic of most bird species with a single clutch of variable size per year. The effect of photoperiod on timing of laying, clutch size, and subsequent molt was investigated in kestrel pairs breeding and raising their young in captivity. In natural daylight (nLD), clutch size, under ad libitum feeding, showed the same decline with date as in nature. Birds breeding later also started molt later and molted faster (more feathers simultaneously), so that all birds completed molt more or less at the same time. Constant long days (LD 17.5:6.5 and LD 13:11) from December 1 onward advanced both reproduction and molt. The LD 17.5:6.5 group developed the reproductive system faster, had a shorter courtship period, and laid eggs earlier than the LD 13:11 group. In both photoperiods there was a decrease in clutch size with progressive laying date, similar to that in nLD. Molt started in both groups at about the end of the laying period and slowed down in the longer photoperiod, especially in males. Plasma luteinizing hormone (LH) changes in the two photoperiods were different for males and females. Males showed the expected slower LH response in the shorter photoperiod, but the initial LH response by females was the same in both photoperiods. Data on LH, reproductive behavior, and body mass suggest that females have a wider annual reproductive window than males. Data on time of laying and number of eggs suggest that clutch size in the kestrel is determined by laying date itself, following an endogenous rhythm that is phase-locked to the reproductive cycle.

Androgens↗