High-quality, large-area MoSe2 and MoSe2/Bi2Se3 heterostructures on AlN(0001)/Si(111) substrates by molecular beam epitaxy.

Atomically-thin, inherently 2D semiconductors offer thickness scaling of nanoelectronic devices and excellent response to light for low-power versatile applications. Using small exfoliated flakes, advanced devices and integrated circuits have already been realized, showing great potential to impact nanoelectronics. Here, high-quality single-crystal MoSe2 is grown by molecular beam epitaxy on AlN(0001)/Si(111), showing the potential for scaling up growth to low-cost, large-area substrates for mass production. The MoSe2 layers are epitaxially aligned with the aluminum nitride (AlN) lattice, showing a uniform, smooth surface and interfaces with no reaction or intermixing, and with sufficiently high band offsets. High-quality single-layer MoSe2 is obtained, with a direct gap evidenced by angle-resolved photoemission spectroscopy and further confirmed by Raman and intense room temperature photoluminescence. The successful growth of high-quality MoSe2/Bi2Se3 multilayers on AlN shows promise for novel devices exploiting the non-trivial topological properties of Bi2Se3.

Physical forces exerted by microbubbles on a surface in a traveling wave field.

The effect of a wave with a varying traveling component on the bubble activity as well as the physical force generated by microbubbles on a surface has been studied. The acoustic emission from a collection of bubbles is measured in a 928 kHz sound field. Particle removal tests on a surface, which actually measures the applied physical force by the bubbles on that surface, indicate a very strong dependence on the angle of incidence. In other words, when the traveling wave component is maximized, the average physical force applied by microbubbles reaches a maximum. Almost complete particle removal for 78 nm silica particles was obtained for a traveling wave, while particle removal efficiency was reduced to only a few percent when a standing wave was applied. This increase in particle removal for a traveling wave is probably caused by a decrease in bubble trapping at nodes and antinodes in a standing wave field.

Enhancement of cavitation activity and particle removal with pulsed high frequency ultrasound and supersaturation.

Megasonic cleaning as applied in leading edge semiconductor device manufacturing strongly relies on the phenomenon of acoustic cavitation. As the occurrence of acoustic cavitation is incorporating a multitude of interdependent effects, the amount of cavitation activity in the cleaning liquid strongly depends on the sonication conditions. It is shown that cavitation activity as measured by means of ultraharmonic cavitation noise can be significantly enhanced when pulsed sonication is applied to a gas supersaturated liquid under traveling wave conditions. It is demonstrated that this enhancement coincides with a dramatic increase in particle removal and is therefore of great interest for megasonic cleaning applications. It is demonstrated that the optimal pulse parameters are determined by the dissolution time of the active bubbles, whereas the amount of cavitation activity depends on the ratio between pulse-off and pulse-on time as well as the applied acoustic power. The optimal pulse-off time is independent of the corresponding pulse-on time but increases significantly with increasing gas concentration. We show that on the other hand, supersaturation is needed to enable acoustic cavitation at aforementioned conditions, but has to be kept below values, for which active bubbles cannot dissolve anymore and are therefore lost during subsequent pulses. For the applicable range of gas contents between 100% and 130% saturation, the optimal pulse-off time reaches values between 150 and 340 ms, respectively. Full particle removal of 78 nm-diameter silica particles at a power density of 0.67 W/cm(2) is obtained for the optimal pulse-off times. The optimal pulse-off time values are derived from the dissolution time of bubbles with a radius of 3.3 µm and verified experimentally. The bubble radius used in the calculations corresponds to the linear resonance size in a 928 kHz sound field, which demonstrates that the recycling of active bubbles is the main enhancement mechanism. The optimal choice of the pulsing conditions however is constrained by the trade-off between the effective sonication time and the desire to have a sufficient amount of active bubbles at lower powers, which might be necessary if very delicate structures have to be cleaned.

Towards an understanding and control of cavitation activity in 1 MHz ultrasound fields.

Various industrial processes such as sonochemical processing and ultrasonic cleaning strongly rely on the phenomenon of acoustic cavitation. As the occurrence of acoustic cavitation is incorporating a multitude of interdependent effects, the amount of cavitation activity in a vessel is strongly depending on the ultrasonic process conditions. It is therefore crucial to quantify cavitation activity as a function of the process parameters. At 1 MHz, the active cavitation bubbles are so small that it is becoming difficult to observe them in a direct way. Hence, another metrology based on secondary effects of acoustic cavitation is more suitable to study cavitation activity. In this paper we present a detailed analysis of acoustic cavitation phenomena at 1 MHz ultrasound by means of time-resolved measurements of sonoluminescence, cavitation noise, and synchronized high-speed stroboscopic Schlieren imaging. It is shown that a correlation exists between sonoluminescence, and the ultraharmonic and broadband signals extracted from the cavitation noise spectra. The signals can be utilized to characterize different regimes of cavitation activity at different acoustic power densities. When cavitation activity sets on, the aforementioned signals correlate to fluctuations in the Schlieren contrast as well as the number of nucleated bubbles extracted from the Schlieren Images. This additionally proves that signals extracted from cavitation noise spectra truly represent a measure for cavitation activity. The cyclic behavior of cavitation activity is investigated and related to the evolution of the bubble populations in the ultrasonic tank. It is shown that cavitation activity is strongly linked to the occurrence of fast-moving bubbles. The origin of this "bubble streamers" is investigated and their role in the initialization and propagation of cavitation activity throughout the sonicated liquid is discussed. Finally, it is shown that bubble activity can be stabilized and enhanced by the use of pulsed ultrasound by conserving and recycling active bubbles between subsequent pulsing cycles.

Time-resolved monitoring of cavitation activity in megasonic cleaning systems.

The occurrence of acoustic cavitation in the cleaning liquid is a crucial precondition for the performance of megasonic cleaning systems. Hence, a fundamental understanding of the impact of different parameters of the megasonic process on cavitation activity is necessary. A setup capable of synchronously measuring sonoluminescence and acoustic emission originating from acoustically active bubbles is presented. The system also includes a high-speed-stroboscopic Schlieren imaging system to directly visualize the influence of cavitation activity on the Schlieren contrast and resolvable bubbles. This allows a thorough characterization of the mutual interaction of cavitation bubbles with the sound field and with each other. Results obtained during continuous sonication of argon-saturated water at various nominal power densities indicate that acoustic cavitation occurs in a cyclic manner, during which periods of stable and inertial cavitation activity alternate. The occurrence of higher and ultraharmonics in the acoustic emission spectra is characteristic for the stable cavitation state. The inertial cavitation state is characterized by a strong attenuation of the sound field, the explosive growth of bubbles and the occurrence of broadband components in the acoustic spectra. Both states can only be sustained at sufficiently high intensities of the sound field. At lower intensities, their occurrences are limited to short, random bursts. Cleaning activity can be linked to the cavitation activity through the measurement of particle removal on standard 200 mm silicon wafers. It is found that the particle removal efficiency is reduced, when a continuous state of cavitation activity ceases to exist.

Cross-sectional study on cytokine polymorphisms, cytokine production after T-cell stimulation and clinical parameters in a random sample of a German population.

We investigated, in a random sample of a German population, the association of polymorphisms in the genes encoding the cytokines interleukin 2 (IL-2), interleukin 4 receptor (IL-4R), interleukin 6 (IL-6), interleukin 10, interferon gamma (IFNG), tumor necrosis factor (TNF) and intercellular adhesion molecule 1 (ICAM-1) with (1) secreted levels of the respective proteins after T-cell stimulation and (2) data on selected diseases obtained from a questionnaire. The scope of this investigation was to further the understanding of the genetic background of allergies and common colds and the observed heterogeneity of many immune responses in the human population. In contrast to previous reports that showed associations of promoter polymorphisms of cytokine genes with the production of the corresponding protein, we did not find associations with protein release after T-cell stimulation in vitro. Among the correlations with the clinical parameters, we observed an increased risk of allergies (odds ratio, OR= 4.1; confidence interval, CI: 1.6-10.4), particularly hay fever (OR=5.6, CI: 1.8-17.1) in individuals homozygous for IFNG 13 CA-repeats. In combination with the TNF wildtype, the risk for hay fever increased to OR=8.4 (CI: 2.7-25.6). Furthermore, individuals with a combination of IL2, IL6 and ICAM-1 polymorphisms tended to have higher frequencies of reported common colds than individuals with the alternate genotypes. As these are results of an explorative investigation, these findings require confirmation in material from a different source. If confirmed, these relationships could contribute to a better characterisation of the genetic component of allergies.

Predialysis urea concentration is sufficient to characterize hemodialysis adequacy.

Mathematical description of urea kinetics for a week showed that, under steady state conditions (i.e., total removal equals total synthesis), any predialysis urea concentration is expressed as a linear function of specific urea generation (G/V) and of dialysis schedule timing and sessional Kt/V (product of clearance, K, and session time, t, divided by the urea distribution volume, V). It also predicts that TACurea is proportional to the predialysis concentrations. The ratio between the two depends linearly on delivered weekly dialysis dose ([wDD] = T(G/V)/TACurea, with T the number of hours in 1 week). These hypotheses have been tested by retrospectively analyzing urea kinetc modelling data that include all predialysis and post dialysis concentrations of 163 patient-weeks. All patients were anuric, and dialysis frequency was thrice weekly. Accuracy is assessed with regression analysis between database numbers and computed values. The theoretical ratio between midweek concentration and TACurea (1.43) is close to the computed ratio (1.46, r2 = 0.909). TACurea (slope = 1.002, r2 = 0.997), specific generation rate G/V as a precursor to PCRn (slope = 1.007, r2 = 0.985), and wDD (slope = 1.002, r2 = 0.909) are all accurately computed from predialysis concentrations. To aid in the determination of the ratio for the different predialysis, concentrations using wDD a nomogram is included.

Target: malnutrition. Results from Tamil Nadu.

PIP: The Tamil Nadu Integrated Nutrition Project (TINP) was highly successful in reducing malnutrition in children by targeting those who needed nutrition the most--children aged 6-36 months. Prior to this project the government was running more than 25 separate programs that were reaching fewer than 10% of the children in this category. TINP integrated nutrition and selected health services. The services were delivered by 2 types of health personnel: multipurpose health workers, and communiy nutrition workers (CNW). CNWs were trained specifically to focus on the at-risk group of 6-36 months. Health workers were responsible for women's health and for children outside the target age group. The 2 groups cooperated with each other through a referral system. Based on growth monitoring information selected children were enrolled in the supplemental program that included daily feeding at the community nutrition center and intensive counseling of mothers. Once children gained weight for at least 90 days they graduated from the feeding program. On average 28% of the children were eligible for the program. 3 out of 5 children graduated within 90 days, and 3 out of 4 graduated in 6 months or less. Overall only 7% of these children returned to a pattern of inadequate growth. Data indicates a 58% decline in the number of at-risk children showing signs of inadequate growth. Results also showed that TINP at an annual cost per person of US$10.96 was less expensive than other government programs.^ieng