Long lifetimes of quantum-dot intersublevel transitions in the terahertz range.

Carrier relaxation is a key issue in determining the efficiency of semiconductor optoelectronic device operation. Devices incorporating semiconductor quantum dots have the potential to overcome many of the limitations of quantum-well-based devices because of the predicted long quantum-dot excited-state lifetimes. For example, the population inversion required for terahertz laser operation in quantum-well-based devices (quantum-cascade lasers) is fundamentally limited by efficient scattering between the laser levels, which form a continuum in the plane of the quantum well. In this context, semiconductor quantum dots are a highly attractive alternative for terahertz devices, because of their intrinsic discrete energy levels. Here, we present the first measurements, and theoretical description, of the intersublevel carrier relaxation in quantum dots for transition energies in the few terahertz range. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to approximately 2 ps at 30 meV (7 THz), in very good agreement with our microscopic theory of the carrier relaxation process. Our studies pave the way for quantum-dot terahertz device development, providing the fundamental knowledge of carrier relaxation times required for optimum device design.

Dioxins and dioxin-like PCBs in different fish from the river Elbe and its tributaries, Germany.

In a long-term program polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) as well as dioxin-like polychlorinated biphenyls (DL-PCBs) were analyzed in the muscle tissue of eels (Anguilla anguilla), bream (Abramis brama), European chub (Leuciscus cephalus) and ide (Leuciscus idus) from the river Elbe and its tributaries Mulde and Saale. The variation of the PCDD/F and DL-PCB concentrations in all fish samples is very large, whereby the DL-PCBs predominate in comparison to the PCDD/Fs. In the eels, the concentrations (pg WHO-TEQ/g ww) for the PCDD/Fs lie in the range of 0.48-22 and for the DL-PCBs between 8.5 and 59. In the whitefish, the concentration range is 0.48-12 for the PCDD/Fs and 1.2-14 for the DL-PCBs. Statistical analysis using relative congener patterns for PCDD/Fs allow spatial correlations to be examined for sub-populations of eels and whitefish. The results are compared to the maximum levels laid down in the European Commission Regulation (EC) No. 466/2001 and the action levels of the European Commission Recommendation 2006/88/EC. Eels caught directly after the major flood in August 2002 as well as eels near Hamburg (years 1996 and 1998) show high concentration peaks. Compared to the eels whitefish is less contaminated with PCDD/Fs and DL-PCBs.

[Quality management in animal welfare]. / Qualitätsmanagement im Bereich Tierschutz (Niedersächsisches System).

In the EC since Jan. 1st 2006 the Regulation (EC) No 882/2004 requires also in the field of animal welfare uniform official controls of a consistently high quality on the basis of documented procedures. Rised demands for the administration necessitate nowadays an all-embracing conception and controlling of the system. Therefore the land of Lower Saxony developed an uniform process-oriented conception for all involved official authorities based on ISO 9001 (EQUINO -Uniform Quality Management in Official Organisations for Consumer Protection in Lower Saxony) and implemented it including a system of internal audits.

Contamination of the alluvial plain, feeding-stuffs and foodstuffs with polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (DL-PCBs) and mercury from the River Elbe in the light of the flood event in August 2002.

Meadow soils, feeding-stuffs and foodstuffs from the alluvial plain of the river Elbe were analyzed in respect of PCDD/Fs, DL-PCBs and mercury with a view to assessing the consequences of the extreme flood of August 2002. The PCDD/F concentrations in the soils range from 3 to 2100 ng WHO-TEQ/kg dm, and for the DL-PCBs the range was 0.32 to 28 ng WHO-TEQ/kg dm. On the basis of established threshold values >40% of the areas are only fit for restricted usage. Mercury concentrations range from 0.11 to 17 mg/kg dm, whereby the action value of 2 mg/kg dm is exceeded in about 50% of the soil samples. A cumulative memory effect from past floods rather than a recent contamination from August 2002 is documented. Soils taken from behind broken dykes showed significantly lower concentrations. Grass, hay and grass silage originating from pasture land in Lower Saxony were taken before and immediately after the flooding. PCDD/Fs range from 0.29 to 16 ng WHO-TEQ/kg, the maximum permitted value of 0.75 ng WHO-TEQ/kg was exceeded in about 50% of the samples. Muscle-tissue from cattle, sheep, lamb and a roe deer as well as untreated milk from individual cows returned values ranging from 0.76 to 5.9 pg WHO-PCDD/F-TEQ/g fat, and 10% of the samples returned values higher than the permitted maximum of 3 pg WHO-PCDD/F-TEQ/g fat. The action value of 2 pg WHO-PCDD/F-TEQ/g fat was exceeded in 33% of the samples. No direct connection between these results and the effects of the flood could be established. A major input path for PCDD/Fs is the tributary Mulde, which discharges contaminated sediments from its catchment area into the Elbe.

Simultaneous time and wavelength resolved spectroscopy under two-colour near infrared and terahertz excitation.

Time and wavelength resolved spectroscopy requires optical sources emitting very short pulses and a fast detection mechanism capable of measuring the evolution of the output spectrum as a function of time. We use table-top Ti:sapphire lasers and a free-electron laser (FEL) emitting ps pulses as excitation sources and a streak camera coupled to a spectrometer for detection. One of the major aspects of this setup is the synchronization of pulses from the two lasers which we describe in detail. Optical properties of the FEL pulses are studied by autocorrelation and electro-optic sampling measurements. We discuss the advantages of using this setup to perform photoluminescence quenching in semiconductor quantum wells and quantum dots. Carrier redistribution due to pulsed excitation in these heterostructures can be investigated directly. Sideband generation in quantum wells is also studied where the intense FEL pulses facilitate the detection of the otherwise weak nonlinear effect.

Fano signatures in the intersubband terahertz response of optically excited semiconductor quantum wells.

Absorption and transmission spectra of broadband terahertz pulses are measured to probe the intersubband response of an optically excited quantum-well heterostructure. While the terahertz absorption shows the single peak of the resonant intersubband transition, the transmission spectra display strong Fano signatures due to the phase sensitive superposition of ponderomotive and terahertz currents as predicted by our microscopic theory.

Anisotropy contrast in phonon-enhanced apertureless near-field microscopy using a free-electron laser.

We demonstrate the imaging of ferroelectric domains in BaTiO3, using an infrared-emitting free-electron laser as a tunable optical source for scattering scanning near-field optical microscopy and spectroscopy. When the laser is tuned into the spectral vicinity of a phonon resonance, ferroelectric domains can be resolved due to the anisotropy of the dielectric properties of the material. Slight detuning of the wavelength gives rise to a contrast reversal clearly evidencing the resonant character of the excitation. The near-field domain contrast shows that the orientation of the dielectric tensor with respect to the sample surface has a clear influence on the near-field signal.

Dioxin concentration in milk and tissues of cows and sheep related to feed and soil contamination.

If cows or sheep are grazing on areas known for a higher dioxin level of the soil, respectively, dry cows are fed with feedstuffs produced on such areas, the dioxin concentration in food, in this case in cows' milk and livers of sheep could reach or exceed maximum levels. Furthermore large amounts of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzo-p-furans (PCDD/F) can be excreted with the faeces. But there are chances for farmers to prevent or at least to minimize the dioxin load of feed and with it of food (including the harvesting technique and the feeding strategy).

Emergency department return visits in chronic obstructive pulmonary disease: the importance of psychosocial factors.

STUDY OBJECTIVES: Relapses are common after treatment of decompensated chronic obstructive pulmonary disease (COPD) in the emergency department. The purpose of this study was to identify psychosocial and pulmonary function variables that distinguish patients who relapse from those who do not. DESIGN: Retrospective case analysis. A relapse was defined as an unscheduled return to the ED within two weeks of treatment. SETTING: 475-bed Veterans Administration Medical Center. TYPE OF PARTICIPANTS: 33 male veterans with COPD who used the ED. MEASUREMENTS: Demographic profile, a Likert-scaled questionnaire about illness beliefs, and physiologic data obtained by chart review. MAIN RESULTS: Patients who relapsed at least once (R patients) were more likely to be widowed, separated, or divorced than patients who did not relapse at any time (N patients) (52.4% vs 8.3%; P = .011). R patients were more likely to have lost a first-order relative within three years (57.1% vs 8.3% P = .006). Stepwise logistic regression showed that the loss of a first-order relative, a negative attitude about prognosis, and a higher forced vital capacity distinguished R from N patients. Stepwise linear regression showed that six specific illness beliefs, distance of the home from the hospital, and baseline bronchodilator response correlated with the number of relapses (multiple r2 = 0.82; P less than .001). CONCLUSION: Social and psychological parameters are closely correlated with relapse in patients with decompensated COPD.

Predicting the need for primary care specialists: the example of a southwestern state.

Because of a need to project the requirements for the training of primary care practitioners in the state of New Mexico, we reviewed available means of determining health manpower needs. Combining several of these methods, we constructed a three-tiered model, taking into account different patterns of care-seeking in areas of various population densities. These methods may be applicable in other states like New Mexico where densely populated cities contrast with sparsely settled rural areas. All such methods, however, are confounded by the state of balance of many factors, including immigration and emigration of physicians, use of nonphysician providers, and patient movement across boundaries for care. This report contributes to the growing literature on health manpower needs by recognizing and attempting to account for differences between urban and rural patterns of care-seeking.