Temperature dependence of open-circuit voltage and recombination processes in polymer-fullerene based solar cells

In this article, we have studied the temperature and illumination dependence of open-circuit voltage (V_OC) in polymer-fullerene based solar cells. It has been observed that V_OC at higher illumination intensities gets converged at 0 K which gives information about maximum achievable V_OC in a particular donor-acceptor blend. Besides this, recombination processes have been studied by transient open-circuit voltage decay (TOCVD) and the transition between recombination regimes has been observed for the first time. At low V_OC carrier lifetime exhibits a constant value around 500 μs, which is interpreted in terms of a monomolecular recombination regime. At higher V_OC carrier lifetime decreases as derived from a bimolecular relaxation law. The method allows estimating the recombination coefficient, which results in 2×10⁻¹³ cm³ s⁻¹. The results have been explained by considering Gaussian density-of-states (DOS) for highest-occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO).     

Techniques for cancellation of interfering multiple reflections in terahertz time-domain measurements

Algorithms are described which allow a significant reduction of the effects of multiple pulses, which originate from pulse reflections within terahertz (THz) emitters. The algorithms are based on models for the pulse propagation inside the emitter. Model parameters can be estimated from a calibration experiment using a reference signal in the absence of a sample. The parameters once estimated for a particular emitter device, can then be used to suppress the effects of multiple pulses in all measurements performed with the same emitter. The application of this method is demonstrated in the investigation of a disc sample and in the investigation of a paint layer.     

Charge Expulsion, Spin Meissner Effect, and Charge Inhomogeneity in Superconductors

Superconductivity occurs in systems that have a lot of negative charge: the highly negatively charged (CuO₂)⁼ planes in the cuprates, negatively charged (FeAs)⁻ planes in the iron arsenides, and negatively charged B ⁻ planes in magnesium diboride. And, in the nearly filled (with negative electrons) bands of almost all superconductors, as evidenced by their positive Hall coefficient in the normal state. No explanation for this charge asymmetry is provided by the conventional theory of superconductivity, within which the sign of electric charge plays no role. Instead, the sign of the charge carriers plays a key role in the theory of hole superconductivity, according to which metals become superconducting because they are driven to expel negative charge (electrons) from their interior. This is why NIS tunneling spectra are asymmetric, with larger current for negatively biased samples. The theory also offers a compelling explanation of the Meissner effect: as electrons are expelled towards the surface in the presence of a magnetic field, the Lorentz force imparts them with azimuthal velocity, thus generating the surface Meissner current that screens the interior magnetic field. In type II superconductors, the Lorentz force acting on expelled electrons that do not reach the surface gives rise to the azimuthal velocity of the vortex currents. In the absence of applied magnetic field, expelled electrons still acquire azimuthal velocity, due to the spin–orbit interaction, in opposite direction for spin-up and spin-down electrons: the “Spin Meissner effect.” This results in a macroscopic spin current flowing near the surface of superconductors in the absence of applied fields, of magnitude equal to the critical charge current (in appropriate units). Charge expulsion also gives rise to an interior outward-pointing electric field and to excess negative charge near the surface. In strongly type II superconductors this physics should give rise to charge inhomogeneity and spin currents throughout the interior of the superconductor, to large sensitivity to (non-magnetic) disorder and to a strong tendency to phase separation.     

Gender differences in myocardial blood flow dynamics: lipid profile and hemodynamic effects

OBJECTIVES: The purpose of the study was to compare myocardial blood flow (MBF) in hyperlipidemic postmenopausal women and age-matched hyperlipidemic men, and to analyze the relationship between cholesterol subfractions and myocardial blood flow in men and women. BACKGROUND: Women are protected from coronary artery disease (CAD) events until well after menopause, in part due to gender-specific differences in lipid profiles. METHODS: To examine the effect of these influences on coronary microcirculation, MBF was quantitated with N-13 ammonia/PET (positron emission tomography) at rest and during adenosine hyperemia in 15 women and 15 men, all nondiabetic, who were matched for age and total cholesterol levels (53+/-4 vs. 50+/-8 years, p = NS, 6.44+/-1.1 vs. 6.31+/-0.85 mmol/liter, or 249+/-41 vs. 244+/-33 mg/dl, p = NS). RESULTS: Women had significantly higher high density lipoprotein (HDL) and lower triglyceride (Tg) levels than did men, and they showed significantly higher resting MBF and stress MBF levels. Significant correlations were found between resting and hyperemic MBF and HDL and Tg levels (r = 0.44, p < 0.02 for stress MBF vs. HDL; r = 0.48, p < 0.007 for stress MBF vs. Tg). Gender was the strongest predictor of hyperemic MBF in multivariate analysis. Women responded to adenosine hyperemia with a significantly higher heart rate than did men, and hemodynamic factors correlated significantly with blood flow both at rest and during stress. CONCLUSIONS: These data suggest that the favorable lipid profile seen in women may be associated with preserved maximal blood flow in the myocardium.     

The identification of markers segregating with resistance to Schistosoma mansoni infection in the snail Biomphalaria glabrata

Both snail and parasite genes determine the susceptibility of the snail Biomphalaria glabrata to infection with the trematode Schistosoma mansoni. To identify molecular markers associated with resistance to the parasite in the snail host, we performed genetic crosses between parasite-resistant and -susceptible isogenic snails. Because resistance to infection in adult snails is controlled by a single locus, DNA samples from individual F2 and F1 backcross progeny, segregating for either the resistant or susceptible phenotypes, were pooled (bulked segregant). Genotypes for both parents were determined with 205 arbitrary decamer primers by random amplified polymorphic DNA-PCR. Of the 205 primers, 144 were informative, and the relative allele frequencies between the pools for these primers were determined. Two primers, OPM-04 and OPZ-11, produced fragments in the resistant parent of one cross that were inherited in a dominant fashion in the resistant F2 and backcross-bulked segregant progeny. Subsequent typing of DNA samples of individual progeny snails showed that the 1.2-kb marker amplified by primer OPM-04 and the 1.0-kb marker produced by primer OPZ-11 segregated in the same dominant fashion with the resistant phenotype. Sequence analysis of the 1.2-kb marker showed that it corresponds to a repetitive sequence in the snail genome with no homology to existing DNA sequences in the public databases. Analysis of the 1. 0-kb marker showed that it also corresponds to a repetitive sequence in the B. glabrata genome that contains an imperfect ORF, with homology to retrovirus-related group-specific antigens (gag) polyprotein.     

Skin cancer in Australian heart transplant recipients

OBJECTIVE: To compare results of a specific capacity assessment administered by the treating clinician, and a Standardized Mini-Mental Status Examination (SMMSE), with the results of expert assessments of patient capacity to consent to treatment. DESIGN: Cross-sectional study with independent comparison to expert capacity assessments. SETTING: Inpatient medical wards at an academic secondary and tertiary referral hospital. PARTICIPANTS: One hundred consecutive inpatients facing a decision about a major medical treatment or an invasive medical procedure. Participants either were refusing treatment, or were accepting treatment but were not clearly capable according to the treating clinician. MEASUREMENTS AND MAIN RESULTS: The treating clinician (medical resident or student) conducted a specific capacity assessment on each participant, using a decisional aid called the Aid to Capacity Evaluation. A specific capacity assessment is a semistructured evaluation of the participant's ability to understand relevant information and appreciate reasonably foreseeable consequences with regard to the specific treatment decision. Participants also received a SMMSE administered by a research nurse. Participants then had two independent expert assessments of capacity. If the two expert assessments disagreed, then an independent adjudication panel resolved the disagreement after reviewing videotapes of both expert assessments. Using the two expert assessments and the adjudication panel as the reference standard, we calculated areas under the receiver-operating characteristic curves and likelihood ratios. The areas under the receiver-operating characteristic curves were 0.90 for specific capacity assessment by treating clinician and 0.93 for SMMSE score (2p =.48). For the treating clinician's specific capacity assessment, likelihood ratios for detecting incapacity were as follows: definitely incapable, 20 (95% confidence interval [CI] 3. 6, 120); probably incapable, 6.1 (95% CI 2.6, 15); probably capable, 0.39 (95% CI 0.18, 0.81); and definitely capable, 0.05 (95% CI 0.01, 0.29). For the SMMSE, a score of 0 to 16 had a likelihood ratio of 15 (95% CI 5.3, 44), a score of 17 to 23 had a likelihood ratio of 0. 68 (95% CI 0.35, 1.2), and a score of 24 to 30 had a likelihood ratio of 0.05 (95% CI 0.01, 0.26). CONCLUSIONS: Specific capacity assessments by the treating clinician and SMMSE scores agree closely with results of expert assessments of capacity. Clinicians can use these practical, flexible, and evaluated measures as the initial step in the assessment of patient capacity to consent to treatment.     

Cervical carcinoma: can dynamic contrast-enhanced MR imaging help predict tumor aggressiveness?

PURPOSE: To determine whether fast dynamic contrast agent-enhanced magnetic resonance (MR) imaging can demonstrate tumor aggressiveness of cervical carcinoma in patients who are eligible for surgical treatment. MATERIALS AND METHODS: Dynamic contrast-enhanced MR imaging of cervical carcinoma was performed in 82 consecutive patients with stage I or IIA disease who were referred for radical hysterectomy. The maximum slope and amplitude of dynamic first-pass contrast enhancement were quantified. These parameters were correlated with histologic measures of tumor aggressiveness (tumor invasion depth, pelvic lymph node status). RESULTS: The analysis was based on tumors in 62 patients: 30 aggressive and 32 relatively nonaggressive tumors. Twenty patients were excluded from analysis owing to insufficient surgical data, tumor too small for accurate assessment, or technical problems. There were no significant differences between aggressive and nonaggressive tumors in terms of the first-pass contrast-enhancement parameters of slope (2.0 vs 2.1 arbitrary signal intensity units per second, P > .5) or amplitude (24.8 vs 27.8 arbitrary units, P > .2). CONCLUSION: Dynamic contrast-enhanced MR imaging does not facilitate differentiation between aggressive and nonaggressive tumors and therefore has no clinical role in assisting in treatment decisions in patients who are candidates for radical hysterectomy.     

The association of initiation factor 4F with poly(A)-binding protein is enhanced in serum-stimulated Xenopus kidney cells

Serum stimulation of cultured Xenopus kidney cells results in enhanced phosphorylation of the translational initiation factor (eIF) 4E and promotes a 2.8-fold increase in the binding of the adapter protein eIF4G to eIF4E, to form the functional initiation factor complex eIF4F. Here we demonstrate the serum-stimulated co-isolation of the poly(A)-binding protein (PABP) with the eIF4F complex. This apparent interaction of PABP with eIF4F suggests that a mechanism shown to be important in the control of translation in the yeast Saccharomyces cerevisiae also operates in vertebrate cells. We also present evidence that the signaling pathways modulating eIF4E phosphorylation and function in Xenopus kidney cells differ from those in several mammalian cell types studied previously. Experiments with the immunosuppressant rapamycin suggest that the mTOR signaling pathway is involved in serum-promoted eIF4E phosphorylation and association with eIF4G. Moreover, we could find little evidence for regulation of eIF4E function via interaction with the specific binding proteins 4E-BP1 or 4E-BP2 in these cells. Although rapamycin abrogated serum-enhanced rates of protein synthesis and the interaction of eIF4G with eIF4E, it did not prevent the increase in association of eIF4G with PABP. This suggests that serum stimulates the interaction between eIF4G and PABP by a distinct mechanism that is independent of both the mTOR pathway and the enhanced association of eIF4G with eIF4E.