The effect of voice lessons on the clinical and perceptual skills of graduate students in speech-language pathology

Two groups of 10 speech-language pathology graduate students were each given 7 weeks of singing lessons to determine whether voice lessons could have an effect on their clinical and perceptual skills. Pre-, mid-, and posttests to measure various skills were designed and implemented. With use of paired sample statistical testing, statistically significant results were obtained. In addition, the subjective responses of the students show that the lessons were effective in improving pitch perception, breath control, and legato production or easy onset. This study supports efforts to integrate curricula in vocal performance and speech-language pathology.     

High-breakdown-voltage AlInAs/GaInAs junction-modulated HEMT's(JHEMT's) with regrown ohmic contacts by MOCVD

A technology for increasing both the two-terminal gate-drain breakdown and subsequently the three-terminal-off-state breakdown of AlInAs/GaInAs high-electron-mobility transistors (HEMTs) to record values without substantial impact on other parameters is presented. The breakdown in these structures is dependent on the multiplication of electrons injected from the source (channel current) and the gate (gate leakage) into the channel. In addition, holes are generated by high fields at the drain and are injected back into the gate and source electrodes. These phenomena can be suppressed by increasing the gate barrier height and alleviating the fields at the drain. Both have been achieved by incorporating a p⁺-2DEG junction as the gate that modulates the 2DEG gas and by utilizing selective regrowth of the source and drain regions by MOCVD. The 1-μm-gate-length devices fabricated have two-terminal gate-drain and three-terminal-off-state breakdown voltages of 31 V and 28 V, respectively     

Synthesis of the carbocyclic analogs of uracil nucleosides

Treatment of the required hydroxyl derivatives of cis-3-aminocyclopentanemethanol with 3-ethoxyacryloyl isocyanate gave N-(3-ethoxyacryloyl)-N′-[hydroxy- or dihydroxy(hydroxy-methyl)cyclopentyl]ureas. Cyclization of the ureas in dilute sulfuric acid afforded high yields of the carbocyclic analogs of uridine, 2′-deoxyuridine, and 3′-deoxyuridine. The uridine and 3′-deoxyuridine analogs were also obtained in good yields by cyclizing the ureas in concentrated aqueous ammonia. None of the three analogs showed activity in tests versus KB cells in culture or L1210 leukemia in vivo.     

Derivatives of 2,4-diamino-6-methylpteridine

Eighteen derivatives of 2,4-diamino-6-methylpteridine related to methotrexate and aminopterin have been prepared from 6-(bromomethyl)-2,4-pteridinediamine by nucleophilic displacement reactions. None of these compounds showed any antileukemic acitivity.     

Folic acid analogs. Modifications in the benzene-ring region. 5. 2′,6′-diazafolic acid

The synthesis of 2′,6′-diazafolic acid was accomplished by the condensation of 2-acetylamino-4(3H)pteridinone-6-earboxaldehyde (XIV) with diethyl N-[(5-amino-2-pyrimidinyl)carbonyl]-L-glutamate (XIII) followed by reduction of the anil double bond and alkaline hydrolylic cleavage of the N²-acetyl and ethyl ester protecting groups. Intermediate XIII was prepared by starling with 5-nitro-2-styrylpyrimidine (VI) and proceeding via 5-arnino-2-styrylpyrimidine (IX). The henzyloxycarbonyl derivative of IX was prepared and oxidized to the corresponding 5-benzyloxycarbonylaminopyrimidine-2-carboxylic acid (XI). The coupling of XI with diethyl L-glutamate followed by hydrogenolysis of the henzyloxycarbonyl function afforded the desired intermediate XIII. 2′,6′-Diazafolic acid was a potent inhibitor of Streptococcus faecium and displayed marginal activity against leukemia 1,1210 in mice.     

The carbocyclic analog of cytidine,synthesis and antineoplastic activity

The carbocyclic analog (VI) of cytidine was prepared from the carbocyclic analog (I) of uridine. The intermediate stages were a tetrabenzoyl derivative of I, the tribenzoyl derivative of the uridine analog, and the tribenzoyl 4-chloropyrimidinone obtained from the latter derivative. The cytidine analog (VI) is active against KB cells in culture and against L1210 leukemia in mice. In the initial tests against L1210 leukemia, the highest dose (200 mg./kg./day, q.d. 1-9), of three active doses, increased lifespan by 82% and showed no evidence of toxicity.     

Organometallic vapor phase epitaxial growth of (AlxGa1-x)0.5In0.5P and its heterostructures

Low pressure organometallic vapor-phase epitaxial growth of Ga_0.5In_0.5P and (Al_xGa_1-x) _0.5In_0.5P is examined. Epitaxial layers of bulk materials are characterized using photoluminescence, electroreflectance, Raman scattering spectroscopy, and surface morphology studies to determine lattice match and optimum growth conditions. Lattice matching at the growth temperature produces featureless growth surfaces, while lattice matching at room temperatures results in minimum photoluminescence linewidth but cracked surfaces due to tensile strain during growth. Raman scattering spectra of the quaternary reveal a three mode structure, with spectral peaks due to GaP-like, InP-like, and AIP-like LO phonons. Heterostructures are investigated including quantum shifts from a series of superlattices. These materials are incorporated in double-heterostructure lasers and single-quantum-well laser with graded-index separate confinement heterostructure     

Influence of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> passivation on surface trapping in SiC metal-semiconductor field-effect transistors

The SiC metal-semiconductor field-effect transistors (MESFETs) have been reported to have current instability and strong dispersion caused by trapping phenomena at the surface and in the substrate, which degrade direct-current (DC) and radio-frequency (RF) performance. This paper illustrates the change in electrical characteristics of SiC MESFETs after Si₃N₄ passivation. Because of a reduction of surface trapping effects, Si₃N₄ passivation can diminish current collapse under pulsed DC conditions, increasing the RF power performance. The reduction of surface trapping effects is verified by the change in the ratio of the drain current to the gate current under pinch-off conditions.     

Effects of SiN passivation and high-electric field on AlGaN-GaN HFET degradation

The authors report on the effects of silicon nitride (SiN) surface passivation and high-electric field stress (hot electron stress) on the degradation of undoped AlGaN-GaN power HFETs. Stressed devices demonstrated a decrease in the drain current and maximum transconductance and an increase in the parasitic drain series resistance, gate leakage, and subthreshold current. The unpassivated devices showed more significant degradation than SiN passivated devices. Gate lag phenomenon was observed from unpassivated devices and removed by SiN passivation. However, SiN passivated devices also showed gate lag phenomena after high-electric field stress, which suggests possible changes in surface trap profiles occurred during high-electric field stress test.     

Effect of cladding layer thickness on the performance ofGaAs-AlGaAs graded index separate confinement heterostructure singlequantum-well lasers

The thinning of cladding layers of GaAs-AlGaAs graded index separate confinement heterostructure single quantum-well (GRINSCH-SQW) lasers offers several advantages. These advantages include easier fabrication of surface grating-based lasers and ridge lasers, the reduction of growth time and source-material use, and the more effective removal of heat due to lower thermal resistance. Experimental results from GRINSCH-SQW lasers showing that typical cladding thicknesses of 1.5 to 2 μm are much thicker than necessary are presented. Lasers with cladding layers as thin as 4500 Å have not shown any increase in threshold current. Theoretical analysis shows good agreement with the experimental results on the minimum cladding thickness necessary to prevent an increase in the threshold current. The differential quantum efficiency is theoretically considered and is found to be more sensitive to cladding-layer thickness