Spontaneous Valley Polarization of Interacting Carriers in a Monolayer Semiconductor.

We report magnetoabsorption spectroscopy of gated WSe_{2} monolayers in high magnetic fields up to 60 T. When doped with a 2D Fermi sea of mobile holes, well-resolved sequences of optical transitions are observed in both σ^{±} circular polarizations, which unambiguously and separately indicate the number of filled Landau levels (LLs) in both K and K^{'} valleys. This reveals the interaction-enhanced valley Zeeman energy, which is found to be highly tunable with hole density p. We exploit this tunability to align the LLs in K and K^{'}, and find that the 2D hole gas becomes unstable against small changes in LL filling and can spontaneously valley polarize. These results cannot be understood within a single-particle picture, highlighting the importance of exchange interactions in determining the ground state of 2D carriers in monolayer semiconductors.

Detection of thermodynamic "valley noise" in monolayer semiconductors: Access to intrinsic valley relaxation time scales.

Together with charge and spin, many novel two-dimensional materials also permit information to be encoded in an electron's valley degree of freedom-that is, in particular momentum states in the material's Brillouin zone. With a view toward valley-based (opto)electronic technologies, the intrinsic time scales of valley scattering are therefore of fundamental interest. Here, we demonstrate an entirely noise-based approach for exploring valley dynamics in monolayer transition-metal dichalcogenide semiconductors. Exploiting their valley-specific optical selection rules, we use optical Faraday rotation to passively detect the thermodynamic fluctuations of valley polarization in a Fermi sea of resident carriers. This spontaneous "valley noise" reveals narrow Lorentzian line shapes and, therefore, long exponentially-decaying intrinsic valley relaxation. Moreover, the noise signatures validate both the relaxation times and the spectral dependence of conventional (perturbative) pump-probe measurements. These results provide a viable route toward quantitative measurements of intrinsic valley dynamics, free from any external perturbation, pumping, or excitation.

Magnetooptics of Exciton Rydberg States in a Monolayer Semiconductor.

We report 65 T magnetoabsorption spectroscopy of exciton Rydberg states in the archetypal monolayer semiconductor WSe_{2}. The strongly field-dependent and distinct energy shifts of the 2s, 3s, and 4s excited neutral excitons permits their unambiguous identification and allows for quantitative comparison with leading theoretical models. Both the sizes (via low-field diamagnetic shifts) and the energies of the ns exciton states agree remarkably well with detailed numerical simulations using the nonhydrogenic screened Keldysh potential for 2D semiconductors. Moreover, at the highest magnetic fields, the nearly linear diamagnetic shifts of the weakly bound 3s and 4s excitons provide a direct experimental measure of the exciton's reduced mass m_{r}=0.20±0.01m_{0}.

The effect of a self-monitoring tool on self-efficacy, health beliefs, and adherence in patients receiving hemodialysis.

OBJECTIVE: Assess the effectiveness of a self-monitoring tool on perceptions of self-efficacy, health beliefs, and adherence in patients receiving hemodialysis. DESIGN: A monthly intervention using a pretest, posttest design over a 6-month period. Both the treatment and control groups were randomly selected and received surveys to assess health beliefs, perceptions of self-efficacy for performing specific healthful behaviors, and renal diet knowledge at baseline, before intervention, and 6 months later. The treatment group also received monthly feedback of monthly phosphorus levels and interdialytic weight gains. SETTING: A university hospital-based 43-chair ambulatory dialysis center. SUBJECTS: Forty patients with end-stage renal disease (25 men and 15 women, age 26 to 78 years), on chronic hemodialysis for at least 2 months and with a history of noncompliance with phosphorus and/or fluid restrictions for 1 or more months. MAIN OUTCOME MEASURES: Self-efficacy, health beliefs, knowledge, biochemical, and demographic variables were analyzed. Analysis of variance tests of repeated measures were used to examine relationships between adherence with phosphorus and fluid restrictions to health beliefs and perceptions of self-efficacy after training in self-monitoring. RESULTS: Overall, there were no significant improvements in adherence with phosphorus and fluid restrictions between the two groups, although a comparison within the groups revealed the treatment group had a statistically significant decrease in mean phosphorus levels of 7.14 to 6.22 mg/dL (P = .005) from baseline to month 3. However, because this value was not maintained, it was not statistically significant. No significant differences existed between the two groups for health beliefs and perceptions of self-efficacy. Knowledge scores in the treatment group, however, improved significantly as compared to the control group (P = .008) and was a significant increase from baseline (P = . 002). In the control group, all scores fell slightly but this difference was not significant. CONCLUSIONS: The benefits of patient self-monitoring and behavioral contracting upon adherence in patients on hemodialysis are inconclusive, as serum phosphorus and interdialytic weight gains did not differ between the two groups. The interventional tools also appeared to have little effect on perceptions of self-efficacy and health beliefs. Trends of improvement, however, did exist for phosphorus within the treatment group and subjects in this group had a statistically significant increase in knowledge scores over time. Additional research using repeated measures design is needed to explore the effects of increased frequency and duration of an intervention on the attainment of patient clinical outcome measures.

African American and white differences in nutritional status among low-income women attending public health clinics.

Information concerning nutritional status and factors influencing dietary intakes among underserved populations is scarce. To obtain this information, data on nutritional status in a group of 726 white and African American women of low education and low income who were inner-city dwellers were analyzed. Dietary habits in all subjects were characterized by high intakes of fat, saturated fat, cholesterol, and salt and low intakes of fiber and folate. A comparison of dietary intake patterns of low-income white and African American women showed a trend toward poorer dietary habits among the white women. It is suggested that differences between African Americans and whites in most nutrient intakes were due to factors such as low levels of education and income rather than racial background alone. Results imply that disease prevention and health promotion programs should include efforts to increase awareness and practice of healthy diet habits among all low-income women.

A case control study of nutritional factors and cervical dysplasia.

The association of nutritional factors with cervical dysplasia was examined through a case-control study. Analysis was conducted in 257 cases and 133 controls confirmed both by cytological examination and colposcopic findings. A 24-h dietary recall questionnaire was used to assess nutritional intake. Various risk factors (including age at first intercourse, number of sexual partners, parity, cigarette smoking, oral contraceptive use, human papillomavirus type 16 infection, and age and race) were adjusted for their potential confounding effects. While analyses were also performed to adjust for total calories, results were not changed significantly. Among the nutrients examined, vitamin A intake showed a significantly increased risk at the lowest quartile compared to the highest quartile, with an odds ratio of 2.2 (95% confidence interval, 1.2-4.2). A significant trend of increasing risk was also observed with lower intake of vitamin A (P = 0.05). Riboflavin showed increased risk at the two lower quartiles of intake with a trend test P value of 0.04. Increased risk was also found for lower intakes of vitamin C compared to the highest intake level. For folate, increased risk was found in the second highest quartile compared with the highest quartile with an odds ratio of 2.0 (95% confidence interval, 1.0-3.8). The calcium:phosphorus ratio showed an increased risk at the lowest level (odds ratio, 2.0; 95% confidence interval, 1.0-4.3). Insufficient intake of vitamin A, riboflavin, ascorbate, and folate is associated with an increased risk of cervical dysplasia.

Evaluation of three nutritional assessment methods in a group of women.

We conducted a reproducibility study of four 24-hour dietary recalls (N = 224) and four biochemical assessments of nutritional status (N = 265) in a group of women in Alabama. For 24-hour recalls, the variance component ratios were all greater than 1, and the intraclass correlation coefficients ranged from 0.16 to 0.27 for macronutrients, and from 0.09 to 0.37 for vitamins and minerals. The intraclass correlation coefficients for biochemical assessments ranged between 0.39 and 0.74 with corresponding variance component ratios of 1 or below for most nutrients. The correlation coefficients between the food frequency questionnaire on the usual dietary intake during the year preceding the beginning of study and the mean values of four 24-hour dietary recalls administered at the initial visit and again after 2, 4, and 6 months ranged from 0.3 to 0.4 for most nutrients. We found plasma beta-carotene levels to be moderately correlated with dietary vitamin A (r = 0.20) and beta-carotene (r = 0.22).