1,890 research outputs found
Transport and recombination through weakly coupled localized spin pairs in semiconductors during coherent spin excitation
Semi-analytical predictions for the transients of spin-dependent transport
and recombination rates through localized states in semiconductors during
coherent electron spin excitation are made for the case of weakly spin-coupled
charge carrier ensembles. The results show that the on-resonant Rabi frequency
of electrically or optically detected spin-oscillation doubles abruptly as the
strength of the resonant microwave field gamma B_1 exceeds the Larmor frequency
separation within the pair of charge carrier states between which the transport
or recombination transition takes place. For the case of a Larmor frequency
separation of the order of gamma B_1 and arbitrary excitation frequencies, the
charge carrier pairs exhibit four different nutation frequencies. From the
calculations, a simple set of equations for the prediction of these frequencies
is derived
Room Temperature Electrical Detection of Spin Coherence in C60
An experimental demonstration of electrical detection of coherent spin motion
of weakly coupled, localized electron spins in thin Fullerene C60 films at room
temperature is presented. Pulsed electrically detected magnetic resonance
experiments on vertical photocurrents through Al/C60/ZnO samples showed that an
electron spin Rabi oscillation is reflected by transient current changes. The
nature of possible microscopic mechanisms responsible for this spin to charge
conversion as well as its implications for the readout of endohedral Fullerene
(N@C60) spin qubits are discussed.Comment: 4 pages, 3 figure
CW and pulsed electrically detected magnetic resonance spectroscopy at 263 GHz/12 T on operating amorphous silicon solar cells
Here we describe a new high frequency/high field continuous wave and pulsed
electrically detected magnetic resonance (CW EDMR and pEDMR) setup, operating
at 263 GHz and resonance fields between 0 and 12 T. Spin dependent transport in
illuminated hydrogenated amorphous silicon p-i-n solar cells at 5 K and 90 K
was studied by in operando 263 GHz CW and pEDMR alongside with complementary
X-band CW EDMR. Benefiting from the superior resolution at 263 GHz, we were
able to better resolve EDMR signals originating from spin dependent hopping and
recombination processes. 5 K EDMR spectra were found to be dominated by
conduction and valence band tale states involved in spin dependent hopping,
with additional contributions from triplet exciton states. 90 K EDMR spectra
could be assigned to spin pair recombination involving conduction band tail
states and dangling bonds as dominating spin dependent transport process, with
additional contributions from valence band tail and triplet exciton states.Comment: 8 pages, 4 figure
Marketing Merit Aid: The Response of Flagship Campuses to State Merit Aid Programs
This article identifies the conundrum that exists between removing financial access barriers to college and the student recipients’ inability to sustain reenrollment. After reviewing the findings of 7 research studies related to the impact of financial aid on persistence, the article concludes with a discussion of possible intervention strategies to employ in conjunction with financial aid packages
Perceived challenges in business development of smallholder dairy farmers in three Malawian regions
Dairy farmers face various challenges in developing their businesses. The current literature identifies several constraints towards a more efficient dairy sector that relate mostly to on-farm management practices. The available studies analyze constraints mostly from the objective viewpoint of the researcher, whereas very little is known about what farmers themselves perceive to be challenging. To better understand the farmers’ perspective and what they perceive to be challenging, and how these challenges differ across regions, this paper builds on a survey of 529 dairy farmers in Malawi. In the survey, respondents were asked in an open question to name their three main challenges. Based on the responses, a three-level coding scheme was elaborated. Data were then coded by two researchers to ensure reliability of coding. Codes were then used to calculate relative frequencies for the different challenges and to perform chi-square tests to check for regional differences in frequencies. Results suggest that farmers perceive low milk price and milk yield, animal health, availability of feedstock, and the costs for drugs as the main challenges. The analysis also revealed that the challenges vary strongly between the three main regions in the country – Blantyre (south), Lilongwe (central), and Mzuzu (north). The perceived challenges reflect the different production systems in the regions. In Blantyre, dairy farming is low in intensity, and farmers thus perceive inputs, in particular the availability of fodder, as well as outputs, in particular milk yields more frequently as a challenge than farmers in Lilongwe and Mzuzu. In contrast, dairy farming in Lilongwe is the most intense. Accordingly, farmers in Lilongwe perceive costs, in particular for inputs such as mash and concentrates as major constraints. Farmers in Mzuzu, which is a rather remote region, consider a lack of assistance, in particular concerning extension services significantly more challenging than the farmers in the other two regions do. Considering these insights, development work and extensions services may be able to increase outcomes in the dairy sector by targeting the regional challenges.Keywords: Challenges, dairy production, smallholders, Malawi, qualitative study, region
Investigations on nucleophilic layers made with a novel plasma jet technique
In this work a novel plasma jet technique is used for the deposition of nucleophilic films based on (3-aminopropyl)trimethoxysilane at atmospheric pressure. Film deposition was varied with regard to duty cycles and working distance. Spectral ellipsometry and chemical derivatization with 4-(trifluoromethyl)benzaldehyde using ATR- FTIR spectroscopy measurements were used to characterize the films. It was found that the layer thickness and the film composition are mainly influenced by the duty cycle
Investigation of hopping transport in n a Si H c Si solar cells with pulsed electrically detected magnetic resonance
Hopping transport through heterostructure solar cells based on B doped crystalline silicon wafers with highly P doped hydrogenated amorphous silicon emitters with different thicknesses is investigated at T 10 K with pulsed electrically detected magnetic resonance. The measurements show that transport is dominated by conduction band tail states g amp; 8776; 2.0046 with a distribution of their mutual coupling strength. The signal intensity correlates to the sample thickness and the g factors do not exhibit an anisotropy which suggests that transport is still dominated by bulk properties of amorphous silicon. In addition, two broad Pdonor hyperfine satellites can be detected. Influences of interface defects such as Pb like states known from silicon dioxide interfaces are either suppressed by the high Fermi energy at the interface or not presen
The ultra-sensitive electrical detection of spin Rabi oscillation at paramagnetic defects
A short review of the pulsed electrically detected magnetic resonance (pEDMR)
experiment is presented. PEDMR allows the highly sensitive observation of
coherent electron spin motion of charge carriers and defects in semiconductors
by means of transient current measurements. The theoretical foundations, the
experimental implementation, its sensitivity and its potential with regard to
the investigation of electronic transitions in semiconductors are discussed.
For the example of the P_b center at the crystalline silicon (111) to silicon
dioxide interface it is shown experimentally how one can detect spin
Rabi-oscillation, its dephasing, coherence decays and spin-coupling effects.Comment: The manuscript has been submitted for journal publicatio
Active vitamin D (1,25-dihydroxyvitamin D) and bone health in middle-aged and elderly men: the European male aging study (EMAS)
<p>Context: There is little information on the potential impact of serum 1,25-dihydroxyvitamin D [1,25(OH)2D] on bone health including turnover.</p>
<p>Objective: The objective of the study was to determine the influence of 1,25(OH)2D and 25-hydroxyvitamin D [25(OH)D] on bone health in middle-aged and older European men.</p>
<p>Design, Setting, and Participants: Men aged 40–79 years were recruited from population registers in 8 European centers. Subjects completed questionnaires that included questions concerning lifestyle and were invited to attend for quantitative ultrasound (QUS) of the heel, assessment of height and weight, and a fasting blood sample from which 1,25(OH)2D, 25(OH)D, and PTH were measured. 1,25(OH)2D was measured using liquid chromatography tandem mass spectrometry. Bone markers serum N-terminal propeptide of type 1 procollagen (P1NP) and crosslinks (β-cTX) were also measured. Dual-energy x-ray absorptiometry (DXA) of the hip and lumbar spine was performed in 2 centers.</p>
<p>Main Outcome Measure(s): QUS of the heel, bone markers P1NP and β-cTX, and DXA of the hip and lumbar spine were measured.</p>
<p>Results: A total of 2783 men, mean age 60.0 years (SD 11.0) were included in the analysis. After adjustment for age and center, 1,25(OH)2D was positively associated with 25(OH)D but not with PTH. 25(OH)D was negatively associated with PTH. After adjustment for age, center, height, weight, lifestyle factors, and season, 1,25(OH)2D was associated negatively with QUS and DXA parameters and associated positively with β-cTX. 1,25(OH)2D was not correlated with P1NP. 25(OH)D was positively associated with the QUS and DXA parameters but not related to either bone turnover marker. Subjects with both high 1,25(OH)2D (upper tertile) and low 25(OH)D (lower tertile) had the lowest QUS and DXA parameters and the highest β-cTX levels.</p>
<p>Conclusions: Serum 1,25(OH)2D is associated with higher bone turnover and poorer bone health despite being positively related to 25(OH)D. A combination of high 1,25(OH)2D and low 25(OH)D is associated with the poorest bone health.</p>
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