Low frequency elastic measurements on solid 4^{4}He in Vycor using a torsional oscillator

Torsional oscillator experiments involving solid $^{4}$He confined in the nanoscale pores of Vycor glass showed anomalous frequency changes at temperatures below 200 mK. These were initially attributed to decoupling of some of the helium's mass from the oscillator, the expected signature of a supersolid. However, these and similar anomalous effects seen with bulk $^{4}$He now appear to be artifacts arising from large shear modulus changes when mobile dislocations are pinned by $^{3}$He impurities. We have used a torsional oscillator (TO) technique to directly measure the shear modulus of the solid $^{4}$He/Vycor system at a frequency (1.2 kHz) comparable to that used in previous TO experiments. The shear modulus increases gradually as the TO is cooled from 1 K to 20 mK. We attribute the gradual modulus change to the freezing out of thermally activated relaxation processes in the solid helium. The absence of rapid changes below 200 mK is expected since mobile dislocations could not exist in pores as small as those of Vycor. Our results support the interpretation of a recent torsional oscillator experiment that showed no anomaly when elastic effects in bulk helium were eliminated by ensuring that there were no gaps around the Vycor sample.Comment: Accepted by Journal of Low Temperature Physic

Dislocation networks in helium-4 crystals

The mechanical behavior of crystals is dominated by dislocation networks, their structure and their interactions with impurities or thermal phonons. However, in classical crystals, networks are usually random with impurities often forming non-equilibrium clusters when their motion freezes at low temperature. Helium provides unique advantages for the study of dislocations: crystals are free of all but isotopic impurities, the concentration of these can be reduced to the ppb level, and the impurities are mobile at all temperatures and therefore remain in equilibrium with the dislocations. We have achieved a comprehensive study of the mechanical response of 4He crystals to a driving strain as a function of temperature, frequency and strain amplitude. The quality of our fits to the complete set of data strongly supports our assumption of string-like vibrating dislocations. It leads to a precise determination of the distribution of dislocation network lengths and to detailed information about the interaction between dislocations and both thermal phonons and 3He impurities. The width of the dissipation peak associated with impurity binding is larger than predicted by a simple Debye model, and much of this broadening is due to the distribution of network lengths.Comment: accepted by Phys. Rev.

Internationalisation, cultural distance and country characteristics: a Bayesian analysis of SME's financial performance

Relying on the accounting data of a panel of 403 Italian manufacturing SMEs collected over a period of 5 years, we find results suggesting that multinationality per se does not impact on the economic performance of international small and medium sized firms. It is the characteristics of the country selected i.e. the political hazard, the financial stability and the economic performance that significantly influence SMEs financial performance. The management implication for small and medium sized firms selecting and entering new geographic markets is significant, since our results show that for SMEs it is the market selection process that really matters and not the degree of multinationality

A cross sectional study of surgical training among United Kingdom general practitioners with specialist interests in surgery

OBJECTIVES: Increasing numbers of minor surgical procedures are being performed in the community. In the UK, general practitioners (family medicine physicians) with a specialist interest (GPwSI) in surgery frequently undertake them. This shift has caused decreases in available cases for junior surgeons to gain and consolidate operative skills. This study evaluated GPwSI's case-load, procedural training and perceptions of offering formalised operative training experience to surgical trainees. DESIGN: Prospective, questionnaire-based cross-sectional study. SETTING/PARTICIPANTS: A novel, 13-item, self-administered questionnaire was distributed to members of the Association of Surgeons in Primary Care (ASPC). A total 113 of 120 ASPC members completed the questionnaire, representing a 94% response rate. Respondents were general practitioners practising or intending to practice surgery in the community. RESULTS: Respondents performed a mean of 38 (range 5–150) surgical procedures per month in primary care. 37% (42/113) of respondents had previously been awarded Membership or Fellowship of a Surgical Royal College; 22% (25/113) had completed a surgical certificate or diploma or undertaken a course of less than 1 year duration. 41% (46/113) had no formal British surgical qualifications. All respondents believed that surgical training in primary care could be valuable for surgical trainees, and the majority (71/113, 63%) felt that both general practice and surgical trainees could benefit equally from such training. CONCLUSIONS: There is a significant volume of surgical procedures being undertaken in the community by general practitioners, with the capacity and appetite for training of prospective surgeons in this setting, providing appropriate standards are achieved and maintained, commensurate with current standards in secondary care. Surgical experience and training of GPwSI's in surgery is highly varied, and does not yet benefit from the quality assurance secondary care surgical training in the UK undergoes. The Royal Colleges of Surgery and General Practice are well placed to invest in such infrastructure to provide long-term, high-quality service and training in the community

Hot stamping of AA6082 tailor welded blanks for automotive applications

Friction stir welded (FSWed) AA6082 tailor welded blanks (TWBs), with gauge combinations of 2.0-2.5 and 3.0-5.0 mm, have been prepared and successfully formed into automotive panel components. Experimental results indicated that the post-form strength, in terms of hardness, varied from location to location on the final parts. The strength is highly dependent on the blank gauges, with the average hardness values being HV 110 and HV 98 for the 2.0-2.5 and 3.0-5.0 mm TWB parts, respectively. Conventional FE simulation was built in PAM-STAMP and the prediction results were validated from experimental data in terms of strain distribution and temperature evolution. A typical continuous cooling precipitation (CCP) diagram for AA6082 was implemented into the verified simulation data to explain the strength variations. It is deemed that the temperature history during the stamping and quenching stages has played a major role on the post-form strength of the final parts

An increase in immature β-cells lacking Glut2 precedes the expansion of β-cell mass in the pregnant mouse

A compensatory increase in β-cell mass occurs during pregnancy to counter the associated insulin resistance, and a failure in adaptation is thought to contribute to gestational diabetes. Insulin-expressing but glucose-transporter-2-low (Ins+Glut2LO) progenitor cells are present in mouse and human pancreas, being predominantly located in extra-islet β-cell clusters, and contribute to the regeneration of the endocrine pancreas following induced ablation. We therefore sought to investigate the contribution of Ins+Glut2LO cells to β-cell mass expansion during pregnancy. Female C57Bl/6 mice were time mated and pancreata were collected at gestational days (GD) 6, 9, 12, 15, and 18, and postpartum D7 (n = 4/time-point) and compared to control (non-pregnant) animals. Beta cell mass, location, proliferation (Ki67+), and proportion of Ins+Glut2LO cells were measured using immunohistochemistry and bright field or confocal microscopy. Beta cell mass tripled by GD18 and β-cell proliferation peaked at GD12 in islets (6 β-cells) and small β-cell clusters (1–5 β-cells). The proportion and fraction of Ins+Glut2LO cells undergoing proliferation increased significantly at GD9 in both islets and clusters, preceding the increase in β-cell mass and proliferation, and their proliferation within clusters persisted until GD15. The overall number of clusters increased significantly at GD9. Quantitative PCR showed a significant increase in Pdx1 presence at GD9 vs. GD18 or control pancreas, and Pdx1 was visualized by immunohistochemistry within both Ins+Glut2LO and Ins+Glut2HI cells within clusters. These results indicate that Ins+Glut2LO cells are likely to contribute to β-cell mass expansion during pregnancy

Decrease in Ins\u3csup\u3e+\u3c/sup\u3eGlut2\u3csup\u3eLO\u3c/sup\u3e β-cells with advancing age in mouse and human pancreas

The presence and location of resident pancreatic β-cell progenitors is controversial. A subpopulation of insulin-expressing but glucose transporter-2-low (Ins+Glut2LO) cells may represent multipotent pancreatic progenitors in adult mouse and in human islets, and they are enriched in small, extra-islet β-cell clusters (\u3e5 β cells) in mice. Here, we sought to identify and compare the ontogeny of these cells in mouse and human pancreata throughout life. Mouse pancreata were collected at postnatal days 7, 14, 21, 28, and at 3, 6, 12, and 18 months of age, and in the first 28 days after β-cell mass depletion following streptozotocin (STZ) administration. Samples of human pancreas were examined during fetal life (22-30 weeks gestation), infancy (0-1 year), childhood (2-9), adolescence (10-17), and adulthood (18-80). Tissues were analyzed by immunohistochemistry for the expression and location of insulin, GLUT2 and Ki67. The proportion of β cells within clusters relative to that in islets was higher in pancreas of human than of mouse at all ages examined, and decreased significantly at adolescence. In mice, the total number of Ins+Glut2LO cells decreased after 7 days concurrent with the proportion of clusters. These cells were more abundant in clusters than in islets in both species. A positive association existed between the appearance of new β cells after the STZ treatment of young mice, particularly in clusters and smaller islets, and an increased proportional presence of Ins+Glut2LO cells during early β-cell regeneration. These data suggest that Ins+Glut2LO cells are preferentially located within β-cell clusters throughout life in pancreas of mouse and human, and may represent a source of β-cell plasticity