On the degrees of freedom of lattice electrodynamics

Using Euler's formula for a network of polygons for 2D case (or polyhedra for 3D case), we show that the number of dynamic\textit{\}degrees of freedom of the electric field equals the number of dynamic degrees of freedom of the magnetic field for electrodynamics formulated on a lattice. Instrumental to this identity is the use (at least implicitly) of a dual lattice and of a (spatial) geometric discretization scheme based on discrete differential forms. As a by-product, this analysis also unveils a physical interpretation for Euler's formula and a geometric interpretation for the Hodge decomposition.Comment: 14 pages, 6 figure

Processing carbon nanotubes with holographic optical tweezers

We report the first demonstration that carbon nanotubes can be trapped and manipulated by optical tweezers. This observation is surprising because individual nanotubes are substantially smaller than the wavelength of light, and thus should not be amenable to optical trapping. Even so, nanotube bundles, and perhaps even individual nanotubes, can be transported at high speeds, deposited onto substrates, untangled, and selectively ablated, all with visible light. The use of holographic optical tweezers, capable of creating hundreds of independent traps simultaneously, suggests opportunities for highly parallel nanotube processing with light.Comment: 3 pages, 1 figur

Expression and characterization of a histidine-rich protein, Hpn: Potential for Ni2+ storage in Helicobacter pylori

Hpn is a small cytoplasmic protein found in Helicobacter pylori, which binds Ni2+ ions with moderate affinity. Consisting of 60 amino acids, the protein is rich in histidine (28 residues, 46.7%), as well as glutamate, glycine and serine residues (in total 31.7%), and contains short repeating motifs. In the present study, we report the detailed biophysical characterization of the multimeric status and Ni2+-binding properties of purified recombinant Hpn under physiologically relevant conditions. The protein exists as an equilibration of multimeric forms in solution, with 20-mers (approx. 136 kDa) being the predominant species. Using equilibrium dialysis, ICP-MS (inductively coupled plasma MS) and UV/visible spectroscopy, Hpn was found to bind five Ni2+ ions per monomer at pH 7.4, with a dissociation constant (Kd) of 7.1 μM. Importantly, Ni2+ binding to Hpn is reversible: metal is released either in the presence of a chelating ligand such as EDTA, or at a slightly acidic pH (pH for half dissociation, pH1/2 ∼6.3). Ni2+ binding induces conformational changes within the protein, increasing β-sheet and reducing α-helical content, from 22% to 37%, and 20% to 10% respectively. Growth curves of Escherichia coli BL21(DE3) both with and without the hpn gene performed under Ni2+ pressure clearly implied a role for Hpn to protect the cells from higher concentrations of external metal ions. Similarly, the accumulation of Ni2+ in these cells expressing Hpn from a plasmid was approx. 4-fold higher than in uninduced controls or control cultures that lacked the plasmid. Similarly, levels of Ni2+ in wild-type H. pylori 26695 cells were higher than those in H. pylori hpn-deletion mutant strains. Hpn may potentially serve multiple roles inside the bacterium: storage of Ni 2+ ions in a 'reservoir'; donation of Ni2+ to other proteins; and detoxification via sequestration of excess Ni2+. © 2006 Biochemical Society.published_or_final_versio

Understanding Medical Mistrust in Black Women at Risk of BRCA 1/2 Mutations

The benefits of genetic counseling and testing for hereditary breast and/or ovarian cancer (HBOC) are well documented; however, Black women are less likely to use these services compared to White women. Mistrust of the medical system has been associated with Black women’s use of genetic counseling and testing (GCT). However, relatively little is known about the correlates of medical mistrust in Black women at increased risk of HBOC. In this study, we examined the prevalence and predictors of medical mistrust in 94 Black women at-risk of HBOC. Most women were married (48.7%) and had at least some collegiate education (57.1%). While no predisposing characteristics were significantly related to medical mistrust, bivariate analysis indicated significant relationships between mistrust and fatalism (p=0.04), perceptions of discrimination in the healthcare setting (p=0.01), and self-efficacy in obtaining GCT (p=0.01). Multivariable analysis revealed that women who reported more discriminatory experiences and women with less confidence in obtaining GCT expressed greater medical mistrust. Multilevel approaches are needed to address psychosocial factors associated with feelings of mistrust. Future efforts must not solely focus on educating women on the importance of and need for GCT; addressing structural barriers, such as patient-provider interactions, that contribute to mistrust must become a priority

Low Digit Ratio Predicts Early Age at Menarche in Colombian Schoolgirls

Background:  The ratio between the lengths of the second and fourth fingers (digit ratio: 2D : 4D), a purported negative correlate of prenatal androgen exposure, has been inversely related to age at menarche. However, a recent study found high digit ratios in carriers of a single variant in the LIN28B gene, which has been linked to delayed menarche. Methods:  We investigated the association of digit ratio and age at menarche in 299 pre‐menarcheal girls aged 5–12 years who participated in a longitudinal cohort study in Bogotá, Colombia. Finger lengths were measured at baseline and the occurrence of menarche was periodically ascertained over a median 32 months of follow‐up. We used time‐to‐event analysis to estimate median ages at menarche as well as hazard ratios for menarche according to tertiles of the digit ratio for each hand. Results:  Estimated median age at menarche was lower for girls in the lowest digit ratio tertile of the right hand compared with those in the highest (12.0 vs. 12.3 years; P ‐value = 0.04). After adjustment for baseline age, height‐ and body mass index‐for‐age z ‐scores, the hazard of menarche was 86% higher in girls of the lowest digit ratio tertile (hazard ratio 1.9 [95% confidence interval 1.2, 2.9]) compared with those in the highest digit ratio tertile of the right hand. No significant associations were found with the left hand. Conclusions:  Digit ratio was positively associated with age at menarche in this longitudinal investigation, consistent with results from a recent gene‐linkage study.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93549/1/j.1365-3016.2012.01310.x.pd

The impact of point mutations in the human androgen receptor : classification of mutations on the basis of transcriptional activity

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