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Sleep restriction has adverse effects on performance and neurobehavioral function. However, the mechanism of impaired performance and neurobehavioral function has not been studied yet.
We examined the effect of insufficient sleep on cerebral blood flow and cognitive function in 8 healthy adults (mean age 22.4 years).
All participants were in bed for 8 h (sufficient sleep), and for < 4 h (insufficient sleep). The oxyhemoglobin (oxyHb) level by a word fluency task was measured with a near-infrared spectroscopy recorder on the morning following sufficient and insufficient sleep periods. Wisconsin card sorting test (WCST), continuous performance test (CPT) and N-back test were evaluated on the same days.
The peak oxyHb level was significantly lower in the left and right frontal lobes after insufficient sleep than after sufficient sleep (left: 0.25 ± 0.10 vs. 0.70 ± 0.29 mmol, P < 0.05; right: 0.23 ± 0.13 vs. 0.73 ± 0.22 mmol, P < 0.05). There was no significant difference in the number of words generated during the word fluency task between sufficient and insufficient sleep states. The percentage of correct responses on CPT after insufficient sleep was significantly lower than that after sufficient sleep (86.6 ± 10.2 vs. 96.0 ± 4.9%, P < 0.05). The reaction time of WCST was significantly longer after insufficient sleep than after sufficient sleep (76.6 ± 13.4 vs. 70.6 ± 16.2 sec, P < 0.05).
One night sleep restriction decreased the concentration changes of oxyHb in brain tissue, leading to impaired cognitive function.
Chronic sleep restriction results from a number of factors; medical condition and social demands, and has adverse effects on daytime function, such as cognitive function and driving performance. We demonstrated that the acute sleep restriction (time in bed < 4 h/night) impaired cortical oxygenation response during word fluency task.
We examined the chronic effect of insufficient sleep on cerebral blood flow and cognitive function.
Ten healthy adults (mean age 19.0 years, mean BMI 22.5 kg/m2) were enrolled in this study. All participants spent > or = 8 h/night in bed prior to study day (sufficient sleep), followed by < 4 h/night in bed for 3 days (insufficient sleep1, 2 and 3). The oxyhemoglobin (oxyHb) level by a word fluency task was measured with a near-infrared spectroscopy recorder on the morning following sufficient and insufficient sleep 1 and 3. Wisconsin card sorting test (WCST), continuous performance test -identical pairs version (CPT-IP) and 2-back test were evaluated on the same day.
The peak oxyHb during the word fluency task was significantly reduced after insufficient sleep 1 and 3 than that after sufficient sleep. The percentage of correct responses on CPT-IP and 2- back test after insufficient sleep 3 were lower than those after sufficient sleep, though there were no significant differences on those. WCST did not significantly differ among insufficient sleep 1 and 3 and sufficient sleep.
The chronic sleep restriction reduced cortical oxygenation response, and might result in cognitive performance impairment.
Metal Organic Decomposition (MOD)-made BaTiO3 (BT) thin films were prepared for Resistive Random Access Memory (ReRAM) under various annealing conditions and investigated for improving the properties of bipolar-type resistive switching, focusing on the relation between oxygen vacancies and the behavior of resistive hysteresis. BT thin films with both pre- and final- annealing in nitrogen showed the resistive hysteresis of bipolar-type switching with current ON/OFF ratios of 2 orders of magnitude for both bias polarities. Finally they showed the endurance property with the 106 switching cycles. It was suggested that oxygen vacancies near the oxide surface (both interfaces at metal electrode/oxide and between layer-by-layered oxide layers) are increased by N2 annealing and enhanced the interface-type resistive switching. Pre-annealing in N2 was also found to be very effective to improve endurance properties, implying that not only the electrode/oxide interface but also the middle part of the film would contribute the interface-type mechanism.
Depression is one of the most prevalent mental illnesses worldwide and a leading cause of disability, especially in the setting of treatment resistance. In recent years, repetitive transcranial magnetic stimulation (rTMS) has emerged as a promising alternative strategy for treatment-resistant depression and its clinical efficacy has been investigated intensively across the world. However, the underlying neurobiological mechanisms of the antidepressant effect of rTMS are still not fully understood. This review aims to systematically synthesize the literature on the neurobiological mechanisms of treatment response to rTMS in patients with depression. Medline (1996–2014), Embase (1980–2014) and PsycINFO (1806–2014) were searched under set terms. Three authors reviewed each article and came to consensus on the inclusion and exclusion criteria. All eligible studies were reviewed, duplicates were removed, and data were extracted individually. Of 1647 articles identified, 66 studies met both inclusion and exclusion criteria. rTMS affects various biological factors that can be measured by current biological techniques. Although a number of studies have explored the neurobiological mechanisms of rTMS, a large variety of rTMS protocols and parameters limits the ability to synthesize these findings into a coherent understanding. However, a convergence of findings suggest that rTMS exerts its therapeutic effects by altering levels of various neurochemicals, electrophysiology as well as blood flow and activity in the brain in a frequency-dependent manner. More research is needed to delineate the neurobiological mechanisms of the antidepressant effect of rTMS. The incorporation of biological assessments into future rTMS clinical trials will help in this regard.
There is an alarming rate of human African trypanosomiasis recrudescence in many parts of sub-Saharan Africa. Yet, the disease has no successful chemotherapy. Trypanosoma lacks the enzymatic machinery for the de novo synthesis of purine nucleotides, and is critically dependent on salvage mechanisms. Inosine 5′-monophosphate dehydrogenase (IMPDH) is responsible for the rate-limiting step in guanine nucleotide metabolism. Here, we characterize recombinant Trypanosoma brucei IMPDH (TbIMPDH) to investigate the enzymatic differences between TbIMPDH and host IMPDH. Size-exclusion chromatography and analytical ultracentrifugation sedimentation velocity experiments reveal that TbIMPDH forms a heptamer, different from type 1 and 2 mammalian tetrameric IMPDHs. Kinetic analysis reveals calculated Km values of 30 and 1300 μm for IMP and NAD, respectively. The obtained Km value of TbIMPDH for NAD is approximately 20–200-fold higher than that of mammalian enzymes and indicative of a different NAD binding mode between trypanosomal and mammalian IMPDHs. Inhibition studies show Ki values of 3·2 μm, 21 nM and 3·3 nM for ribavirin 5′-monophosphate, mycophenolic acid and mizoribine 5′-monophosphate, respectively. Our results show that TbIMPDH is different from its mammalian counterpart and thus may be a good target for further studies on anti-trypanosomal drugs.
The Microlensing Observations in Astrophysics (MOA) is a microlensing survey conducted at Mt. John Observatory in New Zealand. We searched transiting planet candidates from the MOA-I Galactic bulge data, which have been obtained with a 61cm B&C telescope from 2000 to 2005 for a microlensing search. Although this survey data were dedicated to microlensing, they are also quite useful for searching transiting objects because of the large number of stars monitored (~7 million) and the long span of the survey (~6 years). From our analysis, we found 58 transiting planet candidates. We are planning to follow up these candidates with high-precision spectroscopic and photometric observations for further selection, toward the detection of planets by radial velocity observations.
Laser annealed junctions and advanced ultra shallow junctions are studied in both atomistic modeling and experiments. SIMS and sheet resistance measurement for spike-RTA + Laser annealing show that additional laser annealing after spike-RTA (“+Laser”) improve the dopant activation level without increasing in junction depth. “+Laser” effect become effective in the combination of low spike-RTA temperature and high laser temperature. This effect is significant for As doped layer. Spike-RTA based junction has a limitation in viewpoint of Rs-Xj trade-off. Laser-only annealing is promising candidate to overcome this limitation. Boron diffusion with laser-only annealing is investigated. As atomistic kinetic Monte Carlo modeling show that BnIm complexes and End-of-Range (EOR) defects are formed during sub-millisecond annealing time range. Impact of F co-implant on Boron diffusion and EOR defect evolution during sub-millisecond annealing are also investigated.
Photocatalytic hydrogen production with gas-phase reactions in high vacuum was examined for nanocrystalline anatase-type titanium dioxide (TiO2) thin films. The hydrogen generation process on platinized TiO2 specimens was investigated using a quadrupole mass spectrometer at a real-time scale under various partial pressures of gaseous methanol and water. As a result, hydrogen generation was successfully detected under ultraviolet ray (UV) illumination even in high vacuum (∼ 10−7 Torr). And the amount of produced H2 largely depends on the temperature of TiO2 samples, probably due to different surface states of TiO2. This study suggests the possibility of new high-speed H2 production system with gas-phase photocatalytic reactions.
We have investigated the magnetoelectric (ME) properties of the orthorhombic RMnO3 (R=mixed rare earth ions) crystals with and without the 4f magnetic moments, while keeping an average ionic size of R. In the presence of the magnetic contribution from the R ions ((Eu,Ho)MnO3), we have observed the ferroelectric polarization along the c axis (Pc) in a zero field, which arises from the bc spiral structure stabilized by the anisotropic exchange interaction between the R and Mn sublattices like TbMnO3. The Pc phase can be transferred to Pa by application of fields of ∼1.5 T parallel to the b axis. The observed decrease of transition field compared with TbMnO3 suggests that the magnetic contribution and the local distortion of the R ions are key factors for governing the ME properties.
More than 4000 stars observed in both MOA and DENIS projects showing periodic or quasi-periodic light curves are studied. Almost all Mira stars are located on the classical period-luminosity relation, and the multiplicity of the period-luminosity relation is confirmed for small-amplitude stars. The colour-magnitude diagrams based on the MOA red band, Rm, and Ks constructed for the sequences, form a single strip with small successive shifts.
This paper describes the results of extensive performance and reliability characterization of a silicon-based surface micro-machined tunable optical filter. The device comprises a high-finesse Fabry-Perot etalon with one flat and one curved dielectric mirror. The curved mirror is mounted on an electrostatically actuated silicon nitride membrane tethered to the substrate using silicon nitride posts. A voltage applied to the membrane allows the device to be tuned by adjusting the length of the cavity. The device is coupled optically to an input and an output single mode fiber inside a hermetic package. Extensive performance characterization (over operating temperature range) was performed on the packaged device. Parameters characterized included tuning characteristics, insertion loss, filter line-width and side mode suppression ratio. Reliability testing was performed by subjecting the MEMS structure to a very large number of actuations at an elevated temperature both inside the package and on a test board. The MEMS structure was found to be extremely robust, running trillions of actuations without failures. Package level reliability testing conforming to Telcordia standards indicated that key device parameters including insertion loss, filter line-width and tuning characteristics did not change measurably over the duration of the test.
Large (11-mm diameter) single-crystal AlN boules have been prepared using sublimationrecondensation growth. X-ray topography shows that substrates prepared from those boules have a dislocation density of less than 500 cm-2, while the central region of these substrates was nearly dislocation-free. Rocking curves of less than 10 arcsecs have been obtained indicating the high quality of these crystals. The AlN substrates have been used to growth an AlGaN/AlN multiquantum well structure with excellent crystalline quality and with photoluminescence peaked at around 260nm. In addition, a UV LED with emission wavelength at 360nm has been fabricated. This is the first operating opto-electronic device demonstrated on an AlN substrate.
Photoluminescence (PL) and Time-resolved PL (TR-PL) are used to measure the luminescence energy and carrier lifetime of InGaN/GaN quantum well (QW) structures as a function of biaxial strain and excitation density. A blueshift of the transition energy and a decrease in the carrier lifetime reveal a field-dependent spatial electron-hole (e-h) wavefunction separation. This behavior is observed both under the application of tensile, biaxial strain, which directly affects the piezo-related field, and under increased excitation density, which effectively screens the electric field. Our results show an increased carrier separation with increasing QW thickness.
We have explored the growth of GaN on porous SiC substrates by plasma-assisted molecular beam epitaxy. The porous 4H- and 6H-SiC(0001) substrates used in this study contain 10 to 100-nm sized pores and a thin skin layer at the surface. This skin layer was partially removed prior to the growth by H-etching. Transmission electron microscopy (TEM) observations indicate that the epitaxial GaN growth initiates from the surface areas between pores, and the exposed surface pores tend to extend into GaN as open tubes and trap Ga droplets. Plan-view TEM observations indicate that the GaN layers grown on porous substrates contain fewer dislocations than layers grown on non-porous substrates by roughly a factor of two. The GaN layers grown on a porous SiC substrate were also found to be mechanically more relaxed than those grown on non-porous substrates; electron diffraction patterns indicate that the former are free of misfit strain or are even in tension after cooling to room temperature.
A perfect 2D porous alumina photonic crystal with 500 nm interpore distance was fabricated on an area of 4 cm2 via imprint methods and subsequent electrochemical anodization. A 4” imprint stamp consisting of a convex pyramid array was obtained by modern VLSI processing using DUV-lithography, anisotropic etching, LPCVD Si3N4 deposition and wafer bonding. The optical properties of the porous alumina photonic crystal were measured with an infrared microscope in Г-M direction. For both polarizations, a bandgap is observed at around 1 μm for r/a = 0.42. A reflectivity of almost unity for E-polarization in the region of the bandgap is a sign of the high quality of the structure, indicating almost no scattering losses. These experimental results could be correlated very well to the bandstructure as well as reflectivity calculations assuming a dielectric constant of å = 2.0 for the anodized alumina.
Structures and electrical properties of newly synthesized vinylidene fluoride (VDF) oligomer [CF3(CH2CF2)17I] films evaporated onto various substrates around liquid nitrogen temperature were investigated. As a result, the VDF oligomer films were mainly formed with ferroelectric phase (form I) crystals and the molecular chains were oriented parallel to the substrate surfaces regardless of both the kind of the substrates and the thickness of the VDF oligomer films. In addition to these properties, the VDF oligomer films showed polarization reversal due to 180° rotation of the polar VDF oligomer molecules according to the applied voltages. This ferroelectric behavior was verified by local poling and piezoresponse measurements with an atomic force microscope, and by measurements of D-E hysteresis curves.
We studied photoluminescence (PL) of GaN layers grown by molecular beam epitaxy on freestanding high-quality GaN templates. The layers with thickness of ∼ 1 νm were grown under Ga-rich conditions using radio-frequency plasma as a nitrogen source. The PL spectra from both the epilayer and the substrate contain a plethora of very sharp peaks related to excitonic transitions. Through the analysis of the excitonic part of the spectra, we have identified two shallow donors with the binding energies of 28.8 and 32.6 meV, attributed to SiGa and ON, respectively. The PL spectra involved also emissions due to shallow donor-acceptor pair transitions with the main peak at 3.26 eV and a broad band peaking at ∼2.5 - 2.6 eV (green band). The green bands in the GaN substrate and GaN overgrown layer have different energy positions invoking the suggestion that they must have their genesis in different defect centers.
Extended 3D photonic crystals based on macroporous silicon are prepared by applying a periodic variation of the illumination during photoelectrochemical etching. If the lateral pore arrangement is 2D hexagonal, the resulting structure exhibits a simple 3D hexagonal symmetry. The dispersion relation along the pore axis is investigated by optical transmission measurements. Photonic band gaps originating from the pore diameter modulation are observed and the group velocities of the photonic bands are determined by analyzing the Fabry-Perot resonances. Furthermore, angular resolved transmission measurements show a spectral region of omnidirectional total reflectivity.
A Low Thermal Stress (LTS) process, involving the removal of most of the InGaAs(P) material, was used to allow for wafer-fusion of InGaAs(P) samples to Si. The formation and behavior of bubbles of trapped gas between the thinned layer of InGaAs(P) material and the thick Si substrate were studied due to the yield problems such bubbles represent. Observations revealed a low temperature regime <300°C, during which significant gas generation occurred but only weak, reversible bonds were formed. The higher temperature regime, 300°-650°C, was characterized by no significant increase in bubble density, but resulted in a reduction or complete blockage of gas escape during storage. Further investigation of the higher temperature regime indicated continued production of gas, but with a tendency of the gases produced above 300°C to escape from the interface without the formation of bubbles under normal conditions. This information led to the development of a scalable LTS process requiring no modification of the wafers prior to bonding and utilizing sample pre-heating to 300°C before InGaAs(P) removal and subsequent high temperature treatment to 650°C for permanent bond formation.
Si-doped InAsxP1-x layers with As mole fractions ranging from 0.05 to 0.50 were grown on InAsxP1-x step-graded buffer layers on InP substrates by solid source molecular beam epitaxy. The growth parameters consisted of a P:In flux ratio of 7:1, a growth temperature of ∼ 485°C, a growth rate of 2.2 Å/s, and an As:In flux ratio of 0.37-2.36 for varying As mole fractions. The As mole fraction and the layer relaxation were determined using triple axis x-ray diffraction measurements. Near complete relaxation (>93%) was achieved for all Si-doped InAsxP1-x epilayers. The structural morphology indicated that the InAsxP1-x graded buffer layers were effective in relieving the lattice mismatch strain as evidenced by a well-developed crosshatch morphology and low rms surface roughness. The electron concentration, mobility, and Si donor activation energy for each InAsxP1-x composition were determined using temperature dependent Hall measurements. At a constant electron carrier concentration of %3.5×1016 cm-3, the 300 K carrier mobility increased from 2700 to 4732 cm2/V-sec with increasing As mole fraction from 0.05 to 0.50.