Why does a metal-superconductor junction have a resistance?

This is a tutorial article based on a lecture delivered in June 1999 at the NATO Advanced Study Institute in Ankara. The phenomenon of Andreev reflection is introduced as the electronic analogue of optical phase-conjugation. In the optical problem, a disordered medium backed by a phase-conjugating mirror can become completely transparent. Yet, a disordered metal connected to a superconductor has the same resistance as in the normal state. The resolution of this paradox teaches us a fundamental difference between phase conjugation of light and electrons.Comment: 12 pages, 5 postscript figures [v2: all figures inline

Nutrition status of children in a well-child clinic in Lagos Nigeria

The burden of malnutrition is evident around the world and more pronounced in developing countries affecting vulnerable groups such as infants, children under five years of age and pregnant women. This study assessed the nutritional status of infants and children aged 9-59 months who visited a well-child clinic at a teaching hospital in Lagos Nigeria. A descriptive cross-sectional study was conducted on 207 children consecutively recruited at a well-child clinic in 2013. Data was collected using structured interviewer-administered questionnaires. Information collected includes the sociodemographic details of each child and caregiver. In addition, selected anthropometric measurements, biochemical tests comprising serum ferritin and total blood protein levels as well as dietary information for each child participant were obtained by trained data collectors. The sampled children were aged 9-59 months, with slightly over half (53.6%) being 12 months old and above. There were more female children and the number of Fathers 84.1%who had attained tertiary education was higher (84.1%) than that of mothers (76.3%). Serum protein and ferritin levels were less than the normal reference values in 1.8% and 26.2% of the children respectively, while the prevalence of underweight children was 4.9% and 8.1% of the children were overweight based on weight-for-age z-scores. Results from the dietary survey showed that the children consumed fewer proteins than carbohydrates. Furthermore, only 18.8% and 12.6% of parents reported feeding their children fruits and vegetables. Significantly more mothers (97.5%) with tertiary education had children with normal weight for age (P<0.05). Despite the low prevalence of malnutrition among the sampled population, it was found that consumption of fruits and vegetables was low, yet these are major sources of vital micronutrients. Results indicated that the prevalence of malnutrition among the study group was generally low. Therefore, steps must be taken to ensure nutrition specific and nutrition sensitive intervention programs aimed at improving the nutritional status of childrenKey words: Nutritional status, assessment, children, weight, ferritin, protein, diet, malnutrition, clini

Ultimate quantum limit for amplification: A single atom in front of a mirror

We investigate three types of amplification processes for light fields coupling to an atom near the end of a one-dimensional (1D) semi-infinite waveguide. We consider two setups where a drive creates population inversion in the bare or dressed basis of a three-level atom and one setup where the amplification is due to higher-order processes in a driven two-level atom. In all cases, the end of the waveguide acts as a mirror for the light. We find that this enhances the amplification in two ways compared to the same setups in an open waveguide. Firstly, the mirror forces all output from the atom to travel in one direction instead of being split up into two output channels. Secondly, interference due to the mirror enables tuning of the ratio of relaxation rates for different transitions in the atom to increase population inversion. We quantify the enhancement in amplification due to these factors and show that it can be demonstrated for standard parameters in experiments with superconducting quantum circuits

Three "universal" mesoscopic Josephson effects

1. Introduction 2. Supercurrent from Excitation Spectrum 3. Excitation Spectrum from Scattering Matrix 4. Short-Junction Limit 5. Universal Josephson Effects 5.1 Quantum Point Contact 5.2 Quantum Dot 5.3 Disordered Point Contact (Average supercurrent, Supercurrent fluctuations)Comment: 21 pages, 2 figures; legacy revie

TAp63 Is a Master Transcriptional Regulator of Lipid and Glucose Metabolism

SummaryTAp63 prevents premature aging, suggesting a link to genes that regulate longevity. Further characterization of TAp63−/− mice revealed that these mice develop obesity, insulin resistance, and glucose intolerance similar to those seen in mice lacking two key metabolic regulators, Silent information regulator T1 (Sirt1) and AMPK. While the roles of Sirt1 and AMPK in metabolism have been well studied, their upstream regulators are not well understood. We found that TAp63 is important in regulating energy metabolism by accumulating in response to metabolic stress and transcriptionally activating Sirt1, AMPKα2, and LKB1, resulting in increased fatty acid synthesis and decreased fatty acid oxidation. Moreover, we found that TAp63 lowers blood glucose levels in response to metformin. Restoration of Sirt1, AMPKα2, and LKB1 in TAp63−/− mice rescued some of the metabolic defects of the TAp63−/− mice. Our study defines a role for TAp63 in metabolism and weight control

Optimal Experimental Design for Biophysical Modelling in Multidimensional Diffusion MRI

Computational models of biophysical tissue properties have been widely used in diffusion MRI (dMRI) research to elucidate the link between microstructural properties and MR signal formation. For brain tissue, the research community has developed the so-called Standard Model (SM) that has been widely used. However, in clinically applicable acquisition protocols, the inverse problem that recovers the SM parameters from a set of MR diffusion measurements using pairs of short pulsed field gradients was shown to be ill-posed. Multidimensional dMRI was shown to solve this problem by combining linear and planar tensor encoding data. Given sufficient measurements, multiple choices of b-tensor sets provide enough information to estimate all SM parameters. However, in the presence of noise, some sets will provide better results. In this work, we develop a framework for optimal experimental design of multidimensional dMRI sequences applicable to the SM. This framework is based on maximising the determinant of the Fisher information matrix, which is averaged over the full SM parameter space. This averaging provides a fairly objective information metric tailored for the expected signal but that only depends on the acquisition configuration. The optimisation of this metric can be further restricted to any subclass of desirable design constraints like, for instance, hardware-specific constraints. In this work, we compute the optimal acquisitions over the set of all b-tensors with fixed eigenvectors

The NRG1 gene is frequently silenced by methylation in breast cancers and is a strong candidate for the 8p tumour suppressor gene.

Neuregulin-1 (NRG1) is both a candidate oncogene and a candidate tumour suppressor gene. It not only encodes the heregulins and other mitogenic ligands for the ERBB family, but also causes apoptosis in NRG1-expressing cells. We found that most breast cancer cell lines had reduced or undetectable expression of NRG1. This included cell lines that had translocation breaks in the gene. Similarly, expression in cancers was generally comparable to or less than that in various normal breast samples. Many non-expressing cell lines had extensive methylation of the CpG island at the principal transcription start site at exon 2 of NRG1. Expression was reactivated by demethylation. Many tumours also showed methylation, whereas normal mammary epithelial fragments had none. Lower NRG1 expression correlated with higher methylation. Small interfering RNA (siRNA)-mediated depletion of NRG1 increased net proliferation in a normal breast cell line and a breast cancer cell line that expressed NRG1. The short arm of chromosome 8 is frequently lost in epithelial cancers, and NRG1 is the most centromeric gene that is always affected. NRG1 may therefore be the major tumour suppressor gene postulated to be on 8p: it is in the correct location, is antiproliferative and is silenced in many breast cancers

Diaspora entrepreneurs' push and pull institutional factors for investing in Africa: insights from African returnees from the United Kingdom

Applying the institution-based views, this article conceptualises how diaspora entrepreneurs take stimuli from the push and pull institutional factors to develop business enterprises in their countries of origin. Using cases of African diaspora entrepreneurs in the UK and the grounded theory methodological approach, our conceptualised model demonstrates that the diasporas use the new knowledge, skills and wealth they have gained in the UK in tandem with support from trusted family, kinship and business ties at home to develop enterprises. It further demonstrates that diaspora entrepreneurs foster resilience to withstand weak formal institutions in their countries of origin and the discriminatory obstacles in the UK. We also found that institutional barriers which served as push factors that encouraged or forced migrants to leave their home countries to seek greener pastures abroad may later become pull factors that enable them to engage in diaspora entrepreneurship which is often characterised by paradoxes. Particularly, the informal institutions that constrain foreign investors can become assets for African diaspora entrepreneurs and help them set up new businesses and exploit market opportunities in Africa. The implications of the study for diaspora entrepreneurship literature are outlined

Ibrutinib inhibits BTK-driven NF-κB p65 activity to overcome bortezomib-resistance in multiple myeloma

Multiple Myeloma (MM) is a haematologic malignancy characterized by the accumulation of clonal plasma cells in the bone marrow. Over the last 10-15 y the introduction of the proteasome-inhibitor bortezomib has improved MM prognosis, however relapse due to bortezomib-resistance is inevitable and the disease, at present, remains incurable. To model bortezomib-resistant MM we generated bortezomib-resistant MM cell lines (n = 4 ) and utilised primary malignant plasma cells from patients relapsing after bortezomib treatment (n = 6 ). We identified enhanced Bruton's tyrosine kinase (BTK) activity in bortezomib-resistant MM cells and found that inhibition of BTK, either pharmacologically with ibrutinib (0.5 μM) or via lenti-viral miRNA-targeted BTK interference, re-sensitized previously bortezomib-resistant MM cells to further bortezomib therapy at a physiologically relevant concentration (5 nM). Further analysis of pro-survival signaling revealed a role for the NF-κB p65 subunit in MM bortezomib-resistance, thus a combination of BTK and NF-κB p65 inhibition, either pharmacologically or via further lenti-viral miRNA NF-κB p65 interference, also restored sensitivity to bortezomib, significantly reducing cell viability (37.5 ± 6 .9 %, ANOVA P ≤ 0 .001). Accordingly, we propose the clinical evaluation of a bortezomib/ibrutinib combination therapy, including in patients resistant to single-agent bortezomib