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A compact hybrid rocket motor design that incorporates a dual-vortical-flow (DVF) concept is proposed. The oxidizer (nitrous oxide, N2O) is injected circumferentially into various sections of the rocket motor, which are sectored by several solid fuel “rings” (made of hydroxyl-terminated polybutadiene, HTPB) that are installed along the central axis of the motor. The proposed configuration not only increases the residence time of the oxidizer flow, it also implies an inherent “roll control” capability of the motor. Based on a DVF motor geometry with a designed thrust level of 11.6 kN, the characteristics of the turbulent reacting flow within the motor and its rocket performance were analyzed with a comprehensive numerical model that implements both real-fluid properties and finite-rate chemistry. Data indicate that the vacuum specific impulse (Isp) of the DVF motor could reach 278 s. The result from a preliminary ground test of a lab-scale DVF hybrid rocket motor (with a designed thrust level of 3,000 N) also shows promising performance. The proposed DVF concept is expected to partly resolve the issue of scalability, which remains challenging for hybrid rocket motors development.
Aluminum alloys are in high demand for additive manufacturing (AM) processing. However, the physical properties of Al alloys are less favorable for the production of repeatable and reliable parts, with factors such as surface oxide scales, high thermal conductivity, and large solidification shrinkage. Despite these characteristics, processing strategies have been developed to overcome these hurdles. The objective of this article is to highlight the different microstructure–processing–properties characteristics for the three main families of aluminum alloys: pure, casting, and wrought chemistries. The article focuses on AM processes involving solidification, including powder bed and direct energy deposition for both powder and wire feedstock.
Public controversy regarding the potential overdiagnosis and overmedication of children with attention-deficit/hyperactivity disorder (ADHD) has continued for decades. This study used the National Health Insurance Research Database of Taiwan (NHIRD-TW) to explore trends in ADHD diagnosis in youths and the proportion of those receiving medication, with the aim of determining whether ADHD is overdiagnosed and overmedicated in Taiwan.
Youths (age ≤18 years) who had at least two NHIRD-TW claims records with ADHD diagnosis between January 2000 and December 2011 were selected as the subject cohort. In total, the study sample comprised 145 018 patients with ADHD (mean age at a diagnosis of ADHD: 7.7 ± 3.1 years; 21.4% females). The number of cases of ADHD were calculated annually for each year (from 2000 to 2011), and the number of cases per year who received medication was determined as those with at least one record of pharmacotherapy (immediate-release methylphenidate, osmotic controlled-release formulation of methylphenidate, and atomoxetine) in each year.
The prevalence rates of a diagnosis of ADHD in the youths ranged from 0.11% in 2000 to 1.24% in 2011. Compared with children under 6 years of age, the ADHD diagnosis rates in children aged between 7 and 12 years (ratio of prevalence rates = 4.36) and in those aged between 13 and 18 years (ratio of prevalence rates = 1.42) were significantly higher during the study period. The prevalence in males was higher than that in females (ratio of prevalence rates = 4.09). Among the youths with ADHD, 50.2% received medications in 2000 compared with 61.0% in 2011. The probability of receiving ADHD medication increased with age. More male ADHD patients received medications that females patients (ratio of prevalence rates = 1.16).
The rate of ADHD diagnosis was far lower than the prevalence rate (7.5%) identified in a previous community study using face-to-face interviews. Approximately 40–50% of the youths with ADHD did not receive any medications. These findings are not consistent with a systematic public opinion about overdiagnosis or overmedication of ADHD in Taiwan.
We recently demonstrated a sub-bandgap photoresponse with our wafer-scale
Au/TiO2 metallic-semiconductor photonic crystals (MSPhC). The
sub-bandgap energy with 590 nm peak could be absorbed in the form of hot
electron and injected to TiO2, which provides 5.28 times more energy
for photolysis than that of energy absorbed to flat TiO2. If the
solar energy already absorbed above 700 nm could be injected to the catalyst,
higher than 10 times improvement will be achieved, and above 20% solar to fuel
efficiency will be feasible with the robust but inefficient TiO2
catalyst. In order to achieve photocurrent near and above 700 nm spectrum, we
deposited gold nanorods on the surface of MSPhC to incur localized surface
plasmon (LSP) modes absorption and subsequent injection to the TiO2
catalyst. We used electrophoretic deposition (EPD) method to deposit nanorods on
the top, sidewall and bottom well surface of the photonic nanocavities. The
deposition of nanorods was achieved reasonably uniform and sparse not to block
the optical cavities of MSPhC. Flat gold surfaces were tested at 4 different
suspension densities to get the optimum gold nanorods density. Under 10V applied
electric field, positively charged gold nanorods at the concentration of
6.52×1013 #/mL could deposit MSPhC surface
with the density of 230 #/µm2, which was reasonably
uniform and sparse. Preliminary tests show an absorbance increase near 700 nm on
flat device coated with gold nanorods. Photocurrent measurement is under way to
demonstrate the enhanced hot electron transfer over full visible light and
near-infrared solar spectrum.
Information on the risk factors for community-associated skin and soft-tissue infections (SSTIs) due to methicillin-resistant Staphylococcus aureus in Asian populations is scarce. To this end we performed a case-control study of patients treated at two hospital-affiliated outpatient clinics in Taiwan to determine potential risk factors for MRSA SSTIs. S. aureus was isolated from 39 of 100 eligible patients, and 74% were MRSA. Apart from resistance to clindamycin and erythromycin, most MRSA isolates were susceptible to appropriate antimicrobials. The significant risk factors identified by multivariate analysis for MRSA SSTIs were male gender (P = 0·09), nasal carriage of MRSA (P = 0·02), exposure to an individual who had surgery within a year before infection (P = 0·02), and antibiotic treatment for SSTI in the year before infection (P = 0·04). The identification of such factors may assist provision of appropriate treatment to patients with suspected S. aureus SSTIs particularly in Taiwan.
Despite evidence of inhibitory control and visual processing impairment in attention deficit hyperactivity disorder (ADHD), knowledge about its corresponding alterations in the brain is still evolving. The current study used counting Stroop functional MRI and the Cambridge Neuropsychological Test Automated Battery (CANTAB) to investigate if brain activation of inhibitory control and visual processing would differ in youths with ADHD relative to neurotypical youths.
We assessed 25 youths with ADHD [mean age 10.9 (s.d. = 2.2) years] and 23 age-, gender- and IQ-matched neurotypical youths [mean age 11.2 (s.d. = 2.9) years]. The participants were assessed by using the Wechsler Intelligence Scale for Children, third edition, and two tests from the CANTAB: rapid visual information processing (RVP) and pattern recognition memory (PRM) outside the scanner.
Youths with ADHD showed more activation than neurotypical youths in the right inferior frontal gyrus [Brodmann area (BA) 45] and anterior cingulate cortex, which were correlated with poorer performance on the RVP test in the CANTAB. In contrast, youths with ADHD showed less activation than neurotypical youths in the left superior parietal lobule (BA 5/7), which was correlated with the percentage of correct responses on the PRM test in the CANTAB.
Our findings suggest that youths with ADHD might need more inhibitory control to suppress interference between number and meaning and may involve less visual processing to process the numbers in the counting Stroop task than neurotypical youths.
In this study, we use THz spectroscopy in the energy range between 45 GHz to 3000 GHz (1.5 cm-1 and 100 cm-1) as a non-destructive diagnostic tool to characterize the corrosion by-products (rust) on aged steel structural components that are usually embedded in concrete. The THz radiation has been shown to penetrate concrete with extinction coefficients between (1.0 to 2.3) x 10-2 GHz-1 cm-1, depending on the composition and the moisture content of the concrete. The previously reported antiferromagnetic resonance (AFR) near 140 GHz in iron oxide composites was found to be less than our current detection sensitivity (fractional absorbance sensitivity of >10%). However, a strong transition centered near 725 GHz (24 cm-1) has been observed for the first time. This feature has appeared in reflection from several different samples of mildly corroded steel plates and has been tentatively attributed to a broad phonon density of states commonly referred to as the “Boson peak” found in disordered materials. By taking advantage of this strong transition and a powerful excitation sources in the AFR region, we expect THz spectroscopy and imaging to be an effective diagnostic tool with broad applications in corrosion diagnostics and inspection.
We report precise measurements of the fluorine content cF in amorphous silicongermanium alloy films (a-Si, Ge:H, F). The films were prepared by r.f. or d.c. glow discharge deposition. The fluorine concentration was measured by elastic scattering (NES) of 12 MeV protons and by IR absorption spectroscopy. Films measured by NES serve as calibration standards for other measurement techniques. Using the NES measurements, we update the published calibration coefficient for IR measurements for cF ranging from 0 to 10 at.%. The annealing properties up to 700°C of a-Si, Ge:H, F were studied by the gas evolution technique and by IR spectroscopy. Above 300°C the Si-F absorption peak decreases while the peak due to SiF4 molecules increases. No significant loss of F from the alloy films seems to occur up to 700°C.
The formation of Y-Ba-Cu-O phases, including the high Tc superconducting YBa2Cu3O7−x (Y123) phase, during solid state reaction of the mixture of Y2O3: BacO3: CuO, in molar ratio of 0.2:0.6:1 to conform the formula of the perovskite (Y0.4 Ba0.6)CuO3 composition was studied by means of DTA, DTG and X-ray difractometry(XRD). For continuous heating at 10 C/min, it was found that the Y123 phase exists at 790–995 C, and gradually disappears at higher temperatures. The insulating Y2BaCuO5 (Y211) phase exists at 985 to 1190 C, the maximum experiment temperature. While the semiconducting YBa3Cu2O7-y, (Y132) phase coexists with the Y123 phase. For isothermal heating, it was found that the most appropriate temperature and time for the formation of the Y123 phase is 900 C and 16 hours. Semiquantitative data on the amount of phases presented, including the above mentioned phases and other binary Ba-Y-O or Ba-Cu-O phases, during heating are also given. High temperature superconductor with a Tc of around 93 K can be synthesized reproducibly by the processes based on this study.
Deuterated and fluorinated amorphous silicon-germanium alloys, a-Si, Ge:D, F, were studied by Fourier transform infrared (IR) spectroscopy. No Ge.-F modes are observed. The intensity of the Si-F and Si-F2 modes increases with Ge concentration. So does thae intensity of SiF4 which is trapped as isolated molecules. No DF (IR) or F2 (Raman) is observed. The IR spectra of alloys annealed at 300, 400, 500 and 600° C show that the fluorine in the Si-F and Si-F2 groups and in the SiF4 molecules is in thermochemical equilibrium.
The reliability of high performance carbon and beryllium-doped heterojunction bipolar transistors (HBT’s) is investigated using a pulsed mode current stress. After the current stress, the collector current reduction (measured at a fixed Vbe) and the inverted collector current ratio change (measured at two different reverse Vbe biases) are used as measures of HBT degradation due to dopant acceptors migration. For carbon and beryllium doped HBT’s, degradation was found to be only significant beyond a threshold current density (Jth), showing that the carbon doped devices have a higher Jth than that of the Be-doped HBT's. Beyond the Jth, the device degradation is insensitive to the stress current density but depends on the total stress charge. As a result, the device degradation mechanisms of electric field assisted dopant and carrier recombination enhanced dopant migration can be distinguished under pulsed mode current stress.
We measured the diffusion coefficient of H in a-Si:H between 36°C and 690°C via H2-evolution and the pressure rise in a closed ampoule. Our measurement temperatures reached ∼110°C above the highest T reported to date. The diffusion coefficient for unalloyed a-Si:H, DH=1.66×10−3 exp [−1.45 eV/kT] cm2 s−1, agrees with the earlier, lower-T, measurements. Between 250°C and 690°C the H-diffusion mechanism in a-Si:H appears to remain the same, with DH ranging from 10−17 cm2s−1 to 10−10cm 2s−1.
Single crystals of single-phase TiAl alloy (Ti-56 at. % Al) have been grown at lOmm/h solidification rate in an ASGAL FZ-SS35W Optical Floating Zone Furnace. The orientations of the resulting single crystals have been determined using the Laue X-ray diffraction, and Electron Backscattering Pattern (EBSP) methods. A correlation between orientations of the crystal growth and grown-in facets has been established.
Patterned GexSi1−x/Si wells are fabricated for the first time by pulsed laser induced epitaxy technique, employing two different semiconductor processing steps to grow these structures selectively. Two different dimensions of Gt0.12 Si0.55 /Si wells are sucessfully formed, in which one is 3.5 μm wide and 1700Å deep while another is 6 μm wide and 1300Å deep. Transmission electron microscopy combined with energy-dispersive X-ray imaging reveals that the 2-D Ge redistribution profiles are well defined and no significant line or surface defects observed. The 2-D Ge well redistribution behavior, governed by heat and mass transport during laser processing, are also discussed.
Interfacial reactions of polyimide with several metals have been investigated by XPS and TEM to determine their effects on adhesion and long term stability. It has been found that the polyimide-on-metal interface and the metal-on-polyimide interface are intrinsically different; in the case of PI-on-metal interface, the precursor of polyimide, polyamic acid, reacts with the metal resulting in a strong chemical bond and therefore, higher adhesion strength than the corresponding metal-on-PI interface. Both interfaces are found susceptible to T/H environment, resulting in significant adhesion loss. The mechanical and electrical properties of polyimide may be altered as a result of the interaction with metals and therefore, great care is necessary to insure a stable interface and the reliability of devices.
Non-linear optical second harmonic generation (SHG) from bulk silicon is very weak because of the inversion symmetry of the silicon lattice structure. However, when silicon material is subjected to the ion implantation and thermal annealing processes, the inversion symmetry will be broken. As a result, the optical second harmonic generation from the material will increase, and the characteristics of the second harmonic signal are related to the material conditions. In this study, we compare SHG results with Transmission Electron Microscope (TEM) observations for silicon material that has been treated with phosphorous ion implantation and rapid thermal annealing, and suggest that the SHG method may be used for the detection and monitoring of impurities and defects during ion implantation and thermal annealing processes.
We have studied the photoreflectance spectra at 300 K from a series of strained In1−xAlxAs/InP (0.42<x<0.57) strained structures grown by molecular beam epitaxy. From the observed Franz-Keldysh Oscillation we evaluate the built-in de electric field and hence the surface potential under different strain. We found that the surface Fermi level is not pinned at midgap under different strainwhich results in contrast to AIGaAs and GaAs. In addition, from the observed dependence of the built-in electric field Fdc and surface potential barrier Vm on the top layer thickness, we conclude that the surface states are distributed over two separate regions within the energy band gap under different strain and the densities of the surface states are as low as (2,71α0.05)x 1011 cm−2 for the distribution near the conduction band and (4.29α0.05)x1011 cm-2 for the distribution near the valence band. The Fermi level is weakly pinned while the top layer thickness is within the characteristic region of each sample.
This contribution describes the use of layer-by-layer self-limiting siloxane chemisorption processes to self-assemble structurally regular multilayer organic LED (OLED) devices. Topics discussed include: 1) the synthesis of silyl-functionalized precursor molecules for hole transport layer (HTL), emissive layer (EML), and electron transport layer (ETL) self-assembly, 2) the use of layer-by-layer self-assembly for ITO electrode modification/passivation/hole-electron balancing in a vapor-deposited device, 3) the microstructure/chemical characterization of HTL self-assembly using a prototype triarylamine precursor, 4) fabrication and properties of a hybrid self-assembled + vapor deposited two-layer LED, 4) fabrication and properties of a fully self-assembled two-layer OLED.
A monolithic quantum well infrared photodetector (QWIP) structure has been presented that is suitable for dual bands in the two atmospheric transmission windows of 3 – 5.3 μm and 7.5 – 14μm, respectively. The proposed structure employs dual stacked, strain InGaAs/AlGaAs and latticematched GaAs/AlGaAs quantum well infrared photodetector for mid wavelength and long wavelength detection. The response peak of the strain InGaAs/AlGaAs quantum well is at 4.9 μm and the lattice-matched GaAs/AlGaAs is at 10.5μm; their peak sensitivities are in the spectral regions of 3 – 5.3mu;m and 7.5 – 14μm. The peak responsivity when the dual-band QWIP is biased at 5 Volts is ∼0.065A/W at 4.9μm and ∼0.006A/W at 10.5μm; at this voltage the dual-band QWIP is more sensitive at the shorter wavelengths due to its larger impedance thus exhibiting wavelength tunability characteristics with bias. Additionally, single colored 4.9 and 10.5μm QWIPs were fabricated from the dual-band QWIP structure to study the bias-dependent behavior and also to understand the effects of growing the strain layer InGaAs/AlGaAs QWIP on top of the lattice-matched GaAs/AlGaAs QWIP. In summary, two stack dual-band QWIPs using GaAs/AlGaAs and strained InGaAs/AlGaAs multiquantum wells have been demonstrated with peak spectral sensitivities in the spectral region of 3 – 5.3μm and 7.5 – 14μm. Also, the voltage tunable dual-band detection have been realized for this kind of QWIP structure.