Low-noise properties of dry gate recess etched InP HEMTs

Lattice-matched InAlAs-InGaAs HEMTs with dry etched and wet etched gate recesses have been fabricated and both high-frequency and noise measurements have been carried out. The highly selective dry etching process ensures uniform device parameters. The small signal and noise performance shows only minor differences between the two transistor types. There is no evidence of detrimental effects caused by dry etching that reduce the electrical and noise performance of the device at high frequencies. These results show that dry etched InP HEMT's have suitable characteristics for the fabrication of MM-wave integrated circuits     

Influence of cap-layer doping on ohmic contacts for InP based HEMT structures

Ohmic contacts to lattice matched InP based HEMT structures with both doped and undoped GaInAs cap-layers have been investigated. Contact resistances as low as 0.09 Ωmm were achieved using annealed Ni---Ge---Au ohmic contacts. It is reported that the contact resistance is independent of the doping of the thin (50–100 Å) cap-layer. This indicates that it is the bandgap and not the doping of the cap-layer, which determines the contact resistance to the HEMT structure. Furthermore it was shown, that the contact resistance is reduced for lower sheet resistances of the 2DEG.     

Antifungal pharmacodynamic characteristics of fluconazole and amphotericin B tested against Candida albicans

Time-kill curves were determined for three isolates of Candida albicans tested against fluconazole and amphotericin B at multiples of the MIC. Fluconazole produced fungistatic activity, with concentration-related growth effects observed over a narrow range of concentrations. Amphotericin B exhibited fungicidal activity, with enhancement of activity over a broader range of concentrations.     

A validity study of two projective object representations measures.

Two projective measures of object representations, the Concept of the Object on the Rorschach (H. Rorchach, 1942) and the Social Cognition and Object Relations Scales (D. Westen, 1993) were compared with each other, with measures of intelligence (Wechsler Adult Intelligence Scale—Revised; D. Wechsler, 1981), and measures of pathology (Millon Clinical Multiaxial Inventory [T. Millon, 1983], Minnesota Multiphasic Personality Inventory [S. R. Hathaway & J. McKinley, 1983] Axis 11 diagnoses). Analyses focused on the construct validity of object representations and the implications of structural and affective aspects of object representations for psychopathology. Results support the construct validity of object representations and an affective, but not a cognitive–structural, linkage between object representations and pathology. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Analytical bias dependent noise model for InP HEMT's

A practical device model for both high frequency small signal and noise behavior of InP-HEMT's depending on both gate and drain voltage has been developed. The model is based on the two-piece linear approximation using charge control and saturation velocity models. Combining large signal model and analytical expressions for the noise source parameter P, R, and C, an analytical bias-dependent noise model can be obtained. For implementation into high frequency simulation software, the exact calculated bias dependence was mathematically fitted by elementary functions. It could be shown that lowest noise is observed when the drain current for maximum gain is reduced to a third while the drain voltage is reduced to the start of the saturation region V_ds =0.6 V. Modeling scaling effects of the noise behavior shows that lowest noise is observed for a gate width of 1×40 μm. Multi-finger layouts are preferable for gate widths above 70 μm. Furthermore it is shown, that the optimum width of each finger decreases with the number of fingers     

Variation in electrophoretic karyotype and antifungal susceptibility of clinical isolates of Cryptococcus neoformans at a university-affiliated teaching hospital from 1987 to 1994

Ninety-eight isolates of Cryptococcus neoformans were collected from 30 patients at the University of Iowa Hospitals and Clinics from December 1987 through December 1994. The susceptibility of each isolate was determined against fluconazole, itraconazole, amphotericin B, and flucytosine. Of the 98 isolates, 53 were recovered from blood, 19 were recovered from cerebrospinal fluid (CSF), and 26 were recovered from other sources. Although the strains were isolated from the same institution, DNA typing by electrophoretic karyotype (EK) revealed wide genetic variation. Overall, 23 different EK profiles were identified by computer-aided analysis. An isolate exhibiting a single EK was isolated from 24 of 30 patients (80%), whereas multiple strains with unique EKs were isolated from 6 of 30 (20%) patients. Of the six patients who had multiple strains recovered, only one individual had two strains isolated from unique body sites, one strain from the blood and the other from the CSF. Six strains were isolated from multiple patients. Nine patients had multiple sequential isolates recovered over periods of time ranging from 3 days to 4 months. EK analysis revealed persistence of the same genotype in six of the cases. Three patients, however, appeared to have an isolate with a second distinct EK emerge during therapy. Of the patients with sequential positive cultures, an increase in the MICs for test agents was observed in only one case. C. neoformans isolates were collected over a period of 7 years, during which time MICs at our institution remained stable.     

A 10-GHz SiGe BiCMOS phase-locked-loop frequency synthesizer

A SiGe BiCMOS phase-locked-loop (ILL) circuit is presented. A maximum operational frequency of 10 GHz and a current consumption of 7.6 mA, i.e., 17 mW, is demonstrated. For a 9-mW low-power version, a maximum frequency of 4.7 GHz is determined. In a GSM direct conversion application, an in-band phase noise of -79 dBc/Hz at 2 kHz and a spurious suppression of -75 dBc at 400 kHz was measured at 3.4 GHz, which corresponds to a PLL phase noise floor of -214 dBc/Hz. For low-power applications, the PLL can be operated at supply voltages as low as 2.2 V and at RF input powers as low as -20 dBm while having a large output voltage range of 0.2 V to (V_cc-0.3 V). This demonstrates the speed and power advantage of the SiGe BiCMOS over Si BiCMOS and CMOS technologies for wireless communications     

Assessment of antifungal activities of fluconazole and amphotericin B administered alone and in combination against Candida albicans by using a dynamic in vitro mycotic infection model

We evaluated the pharmacodynamic activities of fluconazole and amphotericin B given alone and in combination against Candida albicans by using an in vitro model of bloodstream infection that simulates human serum pharmacokinetic parameters for these antifungals. Fluconazole was administered as a bolus into the model to simulate regimens of 200 mg every 24 h (q24 h) and 400 mg q24 h. Amphotericin B was administered at doses producing the peak concentration (2.4 micrograms/ml) observed with a regimen of 1 mg/kg of body weight q24 h. A combination regimen of fluconazole (400 mg q24 h) and amphotericin B (1 mg/kg q24 h) administered simultaneously and as a staggered regimen (amphotericin B bolus given 8 h after fluconazole bolus) was also simulated in the model to characterize possible antagonism between these agents. Fluconazole alone and amphotericin B alone demonstrated fungistatic (< 99.9% reduction in numbers of CFU per milliliter from the starting inoculum) and fungicidal (> 99.9% reduction) activity, respectively. When fluconazole and amphotericin B were administered simultaneously, fungicidal activity similar to that observed with amphotericin B alone was observed. Staggered administration of fluconazole and amphotericin B, however, resulted in a substantial reduction of the fungicidal activity of amphotericin B, producing fungistatic activity similar to that observed with noncombination fluconazole regimens. These results demonstrate the usefulness of this model for comparing the in vitro pharmacodynamic characteristics of different antifungal regimens and support the theory of azole-polyene antagonism. The effects of this antagonism on the in vivo activity and clinical usefulness of combination antifungal therapy, however, remain to be determined.     

Evaluation of endpoints for antifungal susceptibility determinations with LY303366

We have previously reported poor correlation between the in vitro fungicidal activity of LY303366 and MIC results in RPMI medium based upon the manufacturer's suggested susceptibility endpoint, lack of visual growth. Additionally, we have noted a significant trailing effect with LY303366 when MICs are determined in RPMI medium. These observations have led us to evaluate an alternative susceptibility endpoint for LY303366, an 80% reduction in growth compared with control (similar to that utilized for azoles). Two isolates each of Candida albicans, Candida glabrata, and Candida tropicalis were selected for testing. MICs were determined for LY303366 in RPMI 1640 medium buffered with morpholinepropanesulfonic acid. MICs were determined with suggested (MIC100) and experimental (MIC80) endpoints. The minimal fungicidal concentration (MFC) of LY303366 for each isolate was also determined. Time-kill curves were determined in RPMI medium with each isolate at concentrations of LY303366 ranging from 0.125 to 16x MIC80 to assess the correlation between MIC80 and fungicidal activity. Lastly, fungi exposed to LY303366 were examined via scanning electron microscope (SEM) for evidence of drug-induced ultrastructure change. MIC80s for test isolates ranged from 0.015 to 0.12 microgram/ml and were consistently three to five wells less than MIC100s. Good correlation was observed between fungicidal activity, as assessed by kill curves, and the MIC80. SEM data revealed significant ultrastructure changes induced by LY303366 even at sub-MIC80s. Based on our results demonstrating better correlation between MIC80 and fungicidal activity, i.e., time-kill curves and MFCs, we suggest that 80% reduction in visible growth be utilized as the endpoint for susceptibility determinations with LY303366 in RPMI medium.     

Investigations of thermal crosstalk in laser arrays for WDMapplications

Our studies on the thermal crosstalk of laser arrays with integrated thin-film heaters involved theoretical as well as experimental investigations. Comparing the effects of intentional geometrical variations of the device design, we found that the relative thermal crosstalk depends critically on the distance between the active area and the film heater. The most striking result is that a minimization of the thermal resistivity of the device does not always lead to a reduced thermal crosstalk. We demonstrate that an additional heat barrier close to the active region and/or an improved heat transfer between the submount and the heat sink may reduce the relative thermal crosstalk, a result completely unexpected from intuitive considerations