Electrostatic potential profiles of molecular conductors

The electrostatic potential across a short ballistic molecular conductor depends sensitively on the geometry of its environment, and can affect its conduction significantly by influencing its energy levels and wave functions. We illustrate some of the issues involved by evaluating the potential profiles for a conducting gold wire and an aromatic phenyl dithiol molecule in various geometries. The potential profile is obtained by solving Poisson's equation with boundary conditions set by the contact electrochemical potentials and coupling the result self-consistently with a nonequilibrium Green's function (NEGF) formulation of transport. The overall shape of the potential profile (ramp vs. flat) depends on the feasibility of transverse screening of electric fields. Accordingly, the screening is better for a thick wire, a multiwalled nanotube or a close-packed self-assembled monolayer (SAM), in comparison to a thin wire, a single-walled nanotube or an isolated molecular conductor. The electrostatic potential further governs the alignment or misalignment of intramolecular levels, which can strongly influence the molecular I-V characteristic. An external gate voltage can modify the overall potential profile, changing the current-voltage (I-V) characteristic from a resonant conducting to a saturating one. The degree of saturation and gate modulation depends on the metal-induced-gap states (MIGS) and on the electrostatic gate control parameter set by the ratio of the gate oxide thickness to the channel length.Comment: to be published in Phys. Rev. B 69, No.3, 0353XX (2004

Hormone Therapy and the Risk of Breast Cancer in BRCA1 Mutation Carriers

Background: Hormone therapy (HT) is commonly given to women to alleviate the climacteric symptoms associated with menopause. There is concern that this treatment may increase the risk of breast cancer. The potential association of HT and breast cancer risk is of particular interest to women who carry a mutation in BRCA1 because they face a high lifetime risk of breast cancer and because many of these women take HT after undergoing prophylactic surgical oophorectomy at a young age. Methods: We conducted a matched case-control study of 472 postmenopausal women with a BRCA1 mutation to examine whether or not the use of HT is associated with subsequent risk of breast cancer. Breast cancer case patients and control subjects were matched with respect to age, age at menopause, and type of menopause (surgical or natural). Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated with conditional logistic regression. Statistical tests were two-sided. Results: In this group of BRCA1 mutation carriers, the adjusted OR for breast cancer associated with ever use of HT compared with never use was 0.58 (95% CI = 0.35 to 0.96; P =. 03). In analyses by type of HT, an inverse association with breast cancer risk was observed with use of estrogen only (OR = 0.51, 95% CI = 0.27 to 0.98; P =. 04); the association with use of estrogen plus progesterone was not statistically significant (OR = 0.66, 95% CI = 0.34 to 1.27; P =. 21). Conclusion: Among postmenopausal women with a BRCA1 mutation, HT use was not associated with increased risk of breast cancer; indeed, in this population, it was associated with a decreased risk

The theory, feasibility and accuracy of an ultrasonic method of estimating fetal weight

We present the theory, method, feasibility and accuracy of estimating fetal weight by measuring the fetal volume using compound ultrasonic scanning. The two parameters had a very high coefficient of correlation (0.9794), and the standard error in one series of 20 patients was only ±106 g. The correlation coefficient achieved by one of us who was new to ultrasound techniques was 0.82, which compared favourably with correlations between fetal weight and biparietal diameter measurements (r = 0.26). A discussion as to the correction factors required to allow for the unknown value of the velocity of ultrasound in fetal tissues, the clinical use of this method, and the possible means by which the accuracy of estimating fetal weight may be further improved is included

Effect of monensin inclusion in supplements for cattle consuming low quality tropical forage

A pen feeding study was carried out over 70 days to determine the effects of monensin (M) inclusion in two commercial supplements designed to provide different planes of nutrition to recently weaned steers. Thirty Bos indicus crossbred steers (191.4±s.d. 7.1 kg) were individually fed a low quality pangola grass hay (57 g crude protein/kg DM; 497 g/kg DM digestibility) ad libitum (Control) with either a urea/molasses-based supplement of Rumevite Maxi-graze 60 Block (B), fed at 100 g/day, or grain-based Rumevite Weaner Pellets (WP), fed at 7.5 g/kg liveweight (W).day, both with and without M, viz. B, B+M, WP and WP+M, respectively. There were no significant interactions between supplement type and M inclusion for any measurement. Growth rates (main effects) averaged 0.17, 0.35 and 0.58 kg/day for the Control, B and WP supplements, respectively, with all means different (

The role of handouts in the M.Pharm degree pathway - differentiating between the inquisitive and the acquisitive

Handouts are an established and recognised way for teaching staff to facilitate learning within higher education, by supplementing traditional didactic Learning and Teaching (L&T) methods. Traditionally, teaching in UK Schools of Pharmacy has often relied upon the use of handouts as part of the L&T strategy. However, their use is inconsistent, and dependent upon the teaching style of the educator. To our knowledge, a systematic analysis of their impact on the student learning experience has not been conducted with respect to their use in the Master of Pharmacy (M.Pharm) degree programme. In this article, we survey the attitudes of undergraduate M.Pharm students with respect to the use of handouts and the effect on their learning at two UK schools of pharmacy and compare the results with an Australian (University of Queensland) school of veterinary science. We report that most students' stated preference is for comprehensive learning support in the form of handouts. This is at slight variance with one of our previous works which, although reported a similar result, also reported that there is in some cases an inversely proportional relationship between the number of handouts given to students and the value they place upon them, as well as that students place greater value on material that they have downloaded themselves by means of an intranet or Managed Learning Environment. Two hundred and eighty five School of Pharmacy and Biomolecular Sciences, University of Brighton students (Levels 1-4) and 19 staff responded to questionnaire and 150 School of Pharmacy and Biomolecular Sciences, University of Portsmouth students responded. Reporting from the view that handouts can be a coherent and effective educational strategy to promote lifelong learning, we compare attitudes of the staff and students of the schools and whether or not these influence the manner in which students and staff approach their subjects. We report significant differences in the way five major questions were answered between each school. Comparisons of the responses from the different schools indicated that students from different universities and from both countries have different beliefs regarding handout usage. Eighty-three percent of Brighton students requested comprehensive handouts as an integral component of the lectures, compared to 56% of Queensland students, and 53% of Portsmouth students. Whilst staff favour the limited use of handouts as supplements to lecture materials and tended to agree on most responses, with only 32% of Brighton staff and 34% of Queensland staff agreeing that students should receive comprehensive handouts. More staff than students also agreed that handouts discourage further reading in a subject. Other factors that were significantly related to student responses were gender, year of study, choice of pre-registration field, the presence or absence of a part-time job and whether or not the student was studying in their native country