Current

and optical low-frequency noise of GaInN/GaN green light emitting diode

Observation of the "Memory Steps" in Graphene at Elevated Temperatures

We found that the current-voltage characteristics of the single-layer graphene field-effect transistors exhibit an intriguing feature - an abrupt change of the current near zero gate bias at elevated temperatures T > 500 K. The strength of the effect - referred to as the "memory step" by analogy with the "memory dips" - known phenomenon in electron glasses - depends on the rate of the voltage sweep. The slower the sweep - the more pronounced is the step in the current. Despite differences in examined graphene transistor characteristics, the "memory step" always appears near zero gate bias. The effect is reproducible and preserved after device aging. A similar feature has been previously observed in electronic glasses albeit at cryogenic temperatures and with opposite dependence on the rate of the voltage sweep. The observed "memory step" can be related to the slow relaxation processes in graphene. This new characteristic of electron transport in graphene can be used for applications in high-temperature sensors and switches.Comment: 17 manuscript page

What Can Be Learned from Classical Inventory Models? A Cross-Industry Exploratory Investigation

Classical inventory models offer a variety of insights into the optimal way to manage inventories of individual products. However, top managers and industry analysts are often concerned with the aggregate macroscopic view of a firm's inventory rather than with the inventories of individual products. Given that classical inventory models often do not account for many practical considerations that a company's management faces (e.g., competition, industry dynamics, business cycles, the financial state of the company and of the economy, etc.) and that they are derived at the product level and not the firm level, can insights from these models be used to explain the inventory dynamics of entire companies? This exploratory study aims to address this issue using empirical data. We analyze absolute and relative inventories using a quarterly data panel that contains 722 public U.S. companies for the period 1992-2002. We have chosen companies that are not widely diversified and whose business in large part relies on inventory management to concentrate on empirically testing hypotheses derived from a variety of classical inventory models (economic order quantity (EOQ), [Q, r], newsvendor, periodic review, etc.). We find empirical evidence that firms operating with more uncertain demand, longer lead times, and higher gross margins have larger inventories. Furthermore, larger companies appear to benefit from economies of scale and therefore have relatively less inventory than smaller companies. We obtain mixed evidence on the relationship between inventory levels and inventory holding costs. We also analyze the breakdown of data into eight segments--oil and gas, electronics, wholesale, retail, machinery, hardware, food, and chemicals--and find that, with a few notable exceptions, our hypotheses are supported within the segments as well. Overall, our results demonstrate that many of the predictions from classical inventory models extend beyond individual products to the aggregate firm level; hence, these models can help with high-level strategic choices in addition to tactical decisions.econometrics, panel data, regression analysis, inventory

Chemical Shift and Exchange Interaction Energy of the 1s States of Magnesium Donors in Silicon. The Possibility of Stimulated Emission

Spectroscopy of valley-orbit split-off states in silicon doped by magnesium. Calculation of Relaxation rates of donor states

Prognosis of Thyroid Nodules in Individuals Living in the Zhitomir Region of Ukraine

Objective: After the accident at the Chernobyl Nuclear Power Plant (CNPP), the incidence of thyroid cancer increased among children. Recently, a strong relationship between solid thyroid nodules and the incidence of thyroid cancer was shown in atomic bomb survivors. To assess the prognosis of benign thyroid nodules in individuals living in the Zhitomir region of Ukraine, around the CNPP, we conducted a follow-up investigation of screening data from 1991 to 2000 in the Ukraine. Patients and Methods: Participants of this study were 160 inhabitants with thyroid nodules (nodule group) and 160 inhabitants without thyroid nodules (normal control group) intially identified by ultrasonography from 1991 to 2000. All participants were aged 0 to 10 years old and lived in the same area at the time of the accident. We performed follow-up screening of participants and assessed thyroid nodules by fine needle aspiration biopsy. Results: Among the nodule group participants, the number and size of nodules were significantly increased at the follow-up screening compared with the initial screening. No thyroid nodules were observed among the normal control group participants. The prevalence of thyroid abnormality, especially nodules that could be cancerous (malignant or suspicious by fine needle aspiration biopsy), was 7.5% in the nodule group and 0% in the normal control group (P<0.001). Conclusions: Our study indicated that a thyroid nodule in childhood is a prognostic factor associated with an increase in the number and size of nodules in individuals living in the Zhitomir region of Ukraine