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1

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Enhanced harmonic emission from ionized clusters in intense laser pulses (1997)

Hu, S. X.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 71 (1997), S. 2605-2607

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: We present a two-dimensional model to simulate the enhanced harmonic emission from ionized argon clusters irradiated by an ultrashort (∼25 fs) laser pulse at moderate intensity (∼1014 W/cm2). The low-order harmonics (below the 15th) are enhanced by nearly two orders of magnitude relative to those of monomer argon. Furthermore, the harmonic plateau is extended to a higher frequency. The clustering environment is responsible for the enhancement of harmonic emission. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.119342

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Resonant-cavity InGaAs/InAlGaAs/InP photodetector arrays for wavelength demultiplexing applications (1997)

Hu, S. Y. ; Ko, J. ; Coldren, L. A.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 70 (1997), S. 2347-2349

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: Resonant-cavity photodetector arrays are demonstrated in the InGaAs/InAlAs/InP material system grown by solid-source molecular beam epitaxy. To reduce crosstalk between channels, these devices are designed with a high-Q cavity to obtain narrow-band photoresponse. In addition, a novel double-absorber design has been proposed and implemented to avoid position sensitivity related to the cavity standing wave and eliminate the need for in situ cavity-mode adjustment. Both Schottky and P-i-N diode structures are studied and compared. Eight element arrays with linearly distributed resonant wavelengths spanning over 30 nm are fabricated by using a three-level anodic oxidation process. An experimental channel rejection ratio of 14.5 dB at 4 nm away from the resonant peak has been achieved. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.118870

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3

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Coupled-cavity resonant photodetectors for high-performance wavelength demultiplexing applications (1997)

Hu, S. Y. ; Hegblom, E. R. ; Coldren, L. A.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 71 (1997), S. 178-180

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: A new coupled-cavity resonant photodetector structure is studied to provide a flat-topped passband with steep skirts in the photoresponse. The idea is to add a low-loss cavity that is optically coupled to the absorptive cavity via an intermediate mirror. Experimental reflection spectra confirm this coupling effect. Modeling for an InGaAs/GaAs/AlGaAs design reveals that this new coupled-cavity structure will be able to show a 22 dB channel rejection ratio even when the optical channel spacing is as narrow as 2 nm. In addition, the design and processing tolerances for cavity-mode adjustment are also addressed. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.119523

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4

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Skew angle, media orientation and head-disk spacing change in proximity recording systems : The 41st annual conference on magnetism and magnetic materials (1997)

Liu, B. ; Hu, S. B. ; Soo, K. T. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 81 (1997), S. 4834-4836

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Experiments reported in this work indicate that for the same head-disk spacing, the outer diameter, corresponding to higher skew angle, is more sensitive to the spacing variation. Conducted investigations cover peak detection channels, PRML channels, oriented media, isotropic media, and the same conclusion can be drawn. Increased skew angle will increase the nonlinear transition shift in the write process. Such phenomena can be observed from both the isotropic media and the media with strong orientation.© 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.364742

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5

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Sensitivity study of partial response maximum likelihood and peak detection channels to contamination buildup on air bearing surface of proximity recording sliders : The 41st annual conference on magnetism and magnetic materials (1997)

Liu, B. ; Soo, K. T. ; Hu, S. B. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 81 (1997), S. 5402-5404

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: This work investigates experimentally the sensitivity of partial response maximum likelihood (PRML) and peak detection channels on the increased head-disk spacing caused by the contamination buildup on the slider's air bearing surfaces (ABS). Results obtained indicate that the peak detection channel is sensitive to both the Transition Effect (writing at increased head-disk spacing) and the Readout Resolution Effect (reading at increased head-disk spacing). The increased error rate detected in peak detection channel at increased head-disk spacing can be reduced significantly if the spacing is resumed to normal. In fact, the influence of the transition effect on the peak detection channel is more significant than the readout resolution effect. The PRML channel, however, is mostly sensitive to the transition effect only. The resolution effect, conversely, has rather limited impact on the PRML channel. Off-track sensitivity studies shows that peak shift in the peak detection channel becomes more sensitive to off-track positions when the head-disk spacing is increased. The nonlinear transition shift in the PRML channel, on the contrary, is far less sensitive to the off-track of magnetic head, even when the spacing is increased by the contamination buildup. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.364553

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6

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Microbial Dynamics Associated with Multiphasic Decomposition of 14C-Labeled Cellulose in Soil (1997)

Hu, S. ; van Bruggen, A.H.C.

Springer

Microbial ecology 33 (1997), S. 134 -143

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ISSN: 1432-184X

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Recent emphasis on residue management in sustainable agriculture highlights the importance of elucidating the mechanisms of microbial degradation of cellulose. Cellulose decomposition and its associated microbial dynamics in soil were investigated in incubation experiments. Population dynamics of actinomycetes, bacteria, and fungi were monitored by direct counts. Populations of oligotrophic bacteria in cellulose-amended soil were determined by plate count using a low C medium containing 4 mg C liter−1 agar, and copiotrophs using a high C medium. Cumulative 14CO2 evolution from 14C-labeled cellulose was best described by a multiphasic curve in a 28-day incubation experiment. The initial phase of decomposition was attributed mainly to the activity of bacterial populations with a low oligotroph-to-copiotroph ratio, and the second phase mainly to fungal populations. An increase in oligotroph-to-copiotroph ratio coincided with the emergence of a rapid 14CO2 evolution stage. Streptomycin reduced 14CO2 evolution during the first phase and prompted earlier emergence of the second phase, compared to the control. Cycloheximide initially promoted 14CO2 evolution but subsequently had a lasting negative effect on 14CO2 evolution. Cycloheximide addition significantly increased bacterial biomass and resulted in substantially stronger oscillation of active bacterial populations, whereas it initially reduced, and then stimulated, active fungal biomass. The observed changes in 14CO2 evolution could not be explained by observed shifts in fungal and bacterial biomass, probably because functional groups of fungi and bacteria could not be distinguished. However, it was suggested that oligotrophic bacteria prompted activation of cellulolytic enzumes in fungi and played an important role in leading to fungal dominance of cellulose decomposition.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002489900015

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7

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Bacterial Community Structure in Relation to the Carbon Environments in Lettuce and Tomato Rhizospheres and in Bulk Soil (1997)

Maloney, P.E. ; van Bruggen, A.H.C. ; Hu, S.

Springer

Microbial ecology 34 (1997), S. 109-117

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ISSN: 1432-184X

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Crop roots provide dynamic nutrient environments within agroecosystems that can influence the relative abundance and activity of oligotrophic and copiotrophic microorganisms. Copiotrophic organisms grow in carbon (C)-rich environments and their distribution implies that C abundance favors their survival. Survival of oligotrophic organisms is dependent on their ability to multiply and maintain activity in habitats of low C flux. To determine if spatial variation in available C along the root coincides with different physiological groups of bacteria, we isolated bacteria from the rhizosphere at different locations along the tap root of lettuce and tomato plants grown under greenhouse and field conditions. In all five experiments, the overall numbers of both oligotrophs and copiotrophs were high at the upper portions of the root and lower at tip locations and in the bulk soil environment. Consistent patterns in the ratio of copiotrophic to oligotrophic (C:O) bacteria along the roots of lettuce and tomato were obtained and clearly showed that the C:O ratio was different for these two crop species. With lettuce, C:O ratios were high at the root tip (1.22 to 1.61) and upper mid-root locations (0.90 to 1.30), intermediate at the lower mid-root locations (0.73 to 0.95), and low at the root base (0.56 to 0.76). With tomato, C:O ratios were low at root tip locations (0.50 to 0.68) and high at mid and base locations along the root (1.20 to 1.28). These differences may reflect qualitative and quantitative differences in root exudates between these crop species. In our experiments, nitrogen (N) concentrations and lateral branch sites, providing C sources, were important factors influencing bacterial populations in the rhizosphere of lettuce and tomato. Competitive interactions between microorganisms and physiological constraints with respect to substrate affinity may be two important mechanisms influencing bacterial populations and structure of rhizosphere communities.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002489900040

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8

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Comparison of an in vitro and a damping-off assay to test soils for suppressiveness to Pythium aphanidermatum (1997)

Grünwald, N. J. ; Workneh, F. ; Hu, S. ; [et al.]

Springer

European journal of plant pathology 103 (1997), S. 55-63

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ISSN: 1573-8469

Keywords: cellophane ; conduciveness ; conventional ; cover crops ; damping-off ; Lycopersicon esculentum ; organic ; receptivity ; tomato

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Testing of soil samples in greenhouse assays for suppressiveness to soilborne plant pathogens requires a considerable investment in time and effort as well as large numbers of soil samples. To make it possible to process large numbers of samples efficiently, we compared an in vitro growth assay with a damping-off assay using Pythium aphanidermatum as the test organism on tomato seedlings. The in vitro test compares the radial growth or relative growth of the fungus in soil to that in autoclaved soil and reflects suppressiveness of soils to the pathogen. We used soils from a field experiment that had been farmed either organically or conventionally and into which a cover crop (oats and vetch in mixture) had been incorporated 0, 10, 21, and 35 days previously. We obtained a significant, positive correlation between damping-off severities of tomato seedlings in damping-off assays and both relative and radial growth in vitro. In addition, radial and relative growth of P. aphanidermatum in the in vitro assay were positively correlated with several carbon and nitrogen variables measured for soil and incorporated debris. We did not find differences between the two farming systems for either growth measures of P. aphanidermatum or disease severities on tomato at different stages of cover crop decomposition. The in vitro assay shows potential for use with any fungus that exhibits rapid saprophytic growth, and is most suitable for routine application in suppressiveness testing.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008603006217

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Microbial suppression of in vitro growth of Pythium ultimum and disease incidence in relation to soil C and N availability (1997)

Hu, S. ; van Bruggen, A.H.C. ; Wakeman, R.J. ; [et al.]

Springer

Plant and soil 195 (1997), S. 43-52

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ISSN: 1573-5036

Keywords: carbon and nitrogen availability ; disease incidence ; microbial activity ; microbial biomass C and N ; microbial suppression ; Pythium ultimum

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Experiments were designed to examine effects of the soil microbial community, C and N availability on in vitro growth of Pythium ultimum and its infection of cotton seedlings by manipulating the stage of cellulose decomposition, size and activity of microbial populations, and N availability. In comparison to the untreated control (CONT), cellulose addition alone (CELL) reduced soil nitrate by 35–80 fold, but had no significant effect on soil ammonium. Soil microbial biomass C (SMBC) increased over 2 fold in 14 days following cellulose addition, but significantly decreased in the following 10 days due to N limitation. Addition of both cellulose and N (NCELL) resulted in sustained SMBC for 24 days and significantly reduced in vitro P. ultimum growth and disease incidence. In vitro growth of P. ultimum and disease severity were consistently reduced in the order: CONT 〉 CELL 〉 NCELL. In vitro growth of P. ultimum was lower in soils previously incubated for 24 days than in those incubated for 14 days, and was most closely correlated to cumulative soil CO2 evolution (CO2T). Correlations between P. ultimum growth rates and NO3-N or total available N were substantial (p 〈 0.05), but much less significant than those between the growth rates and SMBC, microbial activity measured as CO2 evolution rates or CO2T (p〈0.0001). Addition of available N (NH4NO3) and C (glucose) just before the assays did not increase the in vitro growth of P. ultimum or disease severity on cotton seedlings, suggesting that time-dependent microbial processes or microbial metabolites significantly contributed to suppression of P. ultimum growth.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1004235411183

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