Two-photon spin injection in semiconductors

A comparison is made between the degree of spin polarization of electrons excited by one- and two-photon absorption of circularly polarized light in bulk zincblende semiconductors. Time- and polarization-resolved experiments in (001)-oriented GaAs reveal an initial degree of spin polarization of 49% for both one- and two-photon spin injection at wavelengths of 775 and 1550 nm, in agreement with theory. The macroscopic symmetry and microscopic theory for two-photon spin injection are reviewed, and the latter is generalized to account for spin-splitting of the bands. The degree of spin polarization of one- and two-photon optical orientation need not be equal, as shown by calculations of spectra for GaAs, InP, GaSb, InSb, and ZnSe using a 14x14 k.p Hamiltonian including remote band effects. By including the higher conduction bands in the calculation, cubic anisotropy and the role of allowed-allowed transitions can be investigated. The allowed-allowed transitions do not conserve angular momentum and can cause a high degree of spin polarization close to the band edge; a value of 78% is calculated in GaSb, but by varying the material parameters it could be as high as 100%. The selection rules for spin injection from allowed-allowed transitions are presented, and interband spin-orbit coupling is found to play an important role.Comment: 12 pages including 7 figure

A Single Charged Quantum Dot in a Strong Optical Field: Absorption, Gain, and the AC Stark Effect

We investigate a singly-charged quantum dot under a strong optical driving field by probing the system with a weak optical field. When the driving field is detuned from the trion transition, the probe absorption spectrum is shifted from the trion resonance as a consequence of the dynamic Stark effect. Simultaneously, a gain sideband is created, resulting from the coherent energy transfer between the optical fields through the quantum dot nonlinearity. As the pump detuning is moved from red to blue, we map out the anticrossing of these two spectral lines. The optical Bloch equations for a stationary two-level atom can be used to describe the numerous spectral features seen in this nano solid state system

Interaction-induced effects in the nonlinear coherent response of quantum-well excitons

Interaction-induced processes are studied using the third-order nonlinear polarization created in polarization-dependent four-wave-mixing experiments (FWM) on a ZnSe single quantum well. We discuss their influence by a comparison of the experimental FWM with calculations based on extended optical Bloch equations including local-field effects, excitation-induced dephasing, and biexciton formation. The investigations show that, for copolarized input fields, excitation-induced dephasing is the dominant FWM mechanism, followed by the conventional density-grating FWM process, biexcitonic contributions, and local-field effects. For cross-linear polarized input fields the excitation-induced dephasing mechanism is canceled so that the conventional density-grating FWM process and biexcitonic contributions are dominating

Reduced blood flow through intrapulmonary arteriovenous anastomoses at rest and during exercise in lowlanders during acclimatization to high altitude

Blood flow through intrapulmonary arteriovenous anastomoses (QIPAVA ) is elevated during exercise at sea level (SL) and at rest in acute normobaric hypoxia. Following high altitude (HA) acclimatization, resting QIPAVA is similar to SL, but it is unknown if this is true during exercise at HA. We reasoned that exercise at HA (5,050 m) would exacerbate QIPAVA due to heightened pulmonary arterial pressure. Using a supine cycle ergometer, seven healthy adults free from intracardiac shunts underwent an incremental exercise test at SL (25, 50, 75% of SL VO2peak ) and at HA (25, 50% of SL VO2peak ). Echocardiography was used to determine cardiac output (Q) and pulmonary artery systolic pressure (PASP) and agitated saline contrast was used to determine QIPAVA (bubble score; 0-5). The principal findings were: (1) Q was similar at SL-rest (3.9 +/- 0.47 l min-1 ) compared with HA-rest (4.5 +/- 0.49 l min-1 ; P = 0.382), but increased from rest during both SL and HA exercise (P < 0.001); (2) PASP increased from SL-rest (19.2 +/- 0.7 mmHg) to HA-rest (33.7 +/- 2.8 mmHg; P = 0.001) and, compared with SL, PASP was further elevated during HA exercise (P = 0.003); (3) QIPAVA was increased from SL-rest (0) to HA-rest (median = 1; P = 0.04) and increased from resting values during SL exercise (P < 0.05), but were unchanged during HA exercise (P = 0.91), despite significant increases in Q and PASP. Theoretical modeling of microbubble dissolution suggests that the lack of QIPAVA in response to exercise at HA is unlikely caused by saline contrast instability

Circulating power: humanitarian logistics, militarism and the United Arab Emirates

While critical authors have interrogated the roots of business logistics, this paper extends the analysis and contributes to a larger critique of the cohering field of Humanitarian Logistics (HL), noting the overlap in the logistical cartographies of militarism and humanitarianism. The focus is on the UAE’s expanding logistics space into the Horn of Africa and the production of specialised HL zones like Dubai International Humanitarian City (DIHC). The article makes three core arguments. First, a logistics lens enables us to expand the study of aid beyond immediate conflict zones, into more distant spaces often constructed as ‘stable’. Second, the placement of logistics at the core of aid delivery has been a key mechanism for inserting market imperatives into humanitarian activities. Third, this gives countries outside the advanced core, such as the UAE, power to leverage and expand their logistics space for multiple purposes, in war making, aid, and commercial activities

QUALITY-OF-LIFE INDICATORS IMPACTING OLDER ADULTS

Radical changes in the senior citizen population have been triggered by the addition of the baby-boomer generation, which drastically increased the growth of this cohort group. A determination of needs for this diverse group of people is necessary for clinical professionals to employ evidence-based practices in the daily provision of services. Purpose: The focus of this study was to measure quality-of-life indicators by concentrating on the association of chronic illness and mental well-being in predicting long-term relationship satisfaction. A sample of older adults were studied in relationship with health and wellness concerns guided by previous research conducted by the Centers for Disease Control and Prevention (CDC, 2011a), and the World Health Organization (1991). Methods: The population selected for this study was older adults participating in outpatient mental health services. A representative sample of 111 participants was used in the statistical analysis of this project. The utilization of the Revised Dyadic Adjustment Scale (Busby, Crane, Larson, & Christensen, 1995) established relationship satisfaction scores among this varied population. Correlation analysis was used to determine the association between seven variables. The factors of interest were: chronic health, chronic pain, mental health acute or chronic, and scores on mental health screenings routinely used in the outpatient mental health clinics included in this study. These variables were broken down in a hierarchical multiple regression model to find out if any factors predicted overall relationship satisfaction. Results: Hierarchical multiple regression analysis delineated an inverse relationship between mental health status (acute or chronic) and degree of overall relationship satisfaction. Chronic health conditions and pain ratings were positively related, however, did not associate negatively with overall relationship satisfaction as hypothesized. Positive relationships were found among the following variables: anxiety ratings and pain-related impairment, increased reports of anxiety with chronic mental health status, and pain ratings with higher risk for suicide. Low correlation coefficient values found throughout the statistical analysis make these findings tentative. Conclusions: The indications of this study confirmed a negative association between chronic mental illness and overall relationship satisfaction scores. This highlights the importance of addressing long-term psychiatric issues as an integral part of working with older adults. Age-related decline creates a functional need for reliance on others complicating satisfaction in intimate partnerships. Mental health practitioners need to be aware of the struggles found among the growing population of older adults to address their treatment and case management needs. Additional research is necessary to determine the indicators of relationship satisfaction impacting quality-of-life among older adults. Key words: quality-of-life, older adults, generational status, chronic illness, chronic pain, mental health, revised dyadic adjustment scale