Effect of spatial distribution and soil volume fertilized on recovery of phosphorus fertilizer by wheat in a pot experiment

Labelled Ca(H₂PO₄)₂ · H₂O was added to two soils (an Oxisol and a vertisol) at two rates, both as a point source and completely dispersed through the soil. The point source treatments included two spatial distributions at each of two percentages of soil volume fertilized. Total and fertilizer phosphorus uptake by wheat (Triticum aestivum) grown for 42 days were determined in a glasshouse experiment. Uptake of fertilizer phosphorus was not affected by spatial distribution, but declined in the Oxisol as percentage soil volume fertilized increased at the low application rate. The implications of these results in terms of the effects of cultivation on fertilizer availability are briefly discussed.     

Distribution of enteric bacteria in Antarctic seawater surrounding a sewage outfall

The spatial distribution and movement of the sewage plume from McMurdo Station, Antarctica, was investigated in the ocean under the early summer sea ice. Ocean currents were also examined to determine their effect on the movement of the plume. Samples of sea water were obtained via holes drilled through the ice and analyzed for coliform bacteria. Coliform densities in ice cores were also determined. Densities of coliform bacteria as high as 10(5)/100 ml were found along the c. 1 km shoreline of McMurdo Station and the plume extended 200-300 m seaward. The relocation of the outfall from a surface configuration to the subsurface (11 m deep) had little influence on the distribution of the plume that sometimes reached the seawater intake station, 400 m to the south. Ocean current measurements in the study area confirmed that, while the prevailing advection was to the north and away from the intake area, episodic reversals of flow at some current meter stations coincided with pulses of sewage that moved to the intake. These findings support the use of bacterial indicators as one means to map the distribution and movement of recent sewage contamination in cold (-1.8 degrees C) sea water and provide evidence that the disposal and movement of domestic wastes deserves attention in coastal [correction of costal] polar environments.     

Side effects of methylphenidate and desipramine alone and in combination in children

OBJECTIVE: To investigate side effects of methylphenidate and desipramine alone and in combination in hospitalized children with symptoms of attention-deficit hyperactivity disorder and depression. METHOD: A double-blind placebo controlled crossover design was used to investigate each medication alone and in combination. Side effect ratings and EKGs were done weekly. Pulse and blood pressure were monitored daily. RESULTS: Nausea, dry mouth, and tremor were present in at least twice as many children on combined methylphenidate and desipramine compared with any other condition. Nausea/vomiting, headaches, other aches, refusal of food, and feeling "tired" were significantly more frequent during the combined methylphenidate plus desipramine condition when compared with either methylphenidate alone or with baseline. Significantly higher ventricular heart rate was found on combined methylphenidate plus desipramine compared with desipramine alone, methylphenidate alone, and baseline. Prolonged PR interval and significantly higher heart rate occurred during desipramine alone compared with baseline. CONCLUSIONS: During the several-month duration of the study, there were more frequent side effects during combined methylphenidate plus desipramine treatment than with either medication alone. Clinically, side effects present during combined medication appeared to be similar to and no more serious than those associated with desipramine alone.     

Alterations in visual receptive fields in the superior colliculus induced by amphetamine

Visual response properties were examined in the superficial layers of the superior colliculus (SC) of anesthetized, paralyzed cats before and after i.v. administration of d-amphetamine. Receptive fields (RFs) of single SC units were plotted using small spots of light presented to the contralateral eye. Within the first hour following d-amphetamine injections, RF size gradually increased, reaching a maximum 86 min post-injection. On average, the area of the RF increased by 5.6 times and RF expansion was observed in all single units examined in the superficial layers. Over the subsequent 4-8 h following the injection, RF area gradually decreased and returned to control dimensions. Most RFs displayed asymmetrical patterns of expansion, showing relatively more horizontal than vertical growth. As RF expansion developed, responses to stimuli flashed "on" and "off" at various locations both inside and outside the borders of the control RF became progressively more vigorous. In contrast, no significant changes were noted in direction-selective responses at any time after d-amphetamine injections. Using an array of light bar stimuli of different lengths, the strength of surround suppression was found to be significantly diminished by d-amphetamine. The reduction in surround suppression was especially clear for bar lengths which exceeded the diameter of the control RF. No RF expansion was observed in the superficial layers of the SC when d-amphetamine was injected intravitreally. Furthermore, d-amphetamine had no discernable effect on the RF sizes of cells in the visual cortex. These results suggest that the RF changes in the SC were not of either retinal or cortical origin. We conclude that the mean retinal area which can potentially influence the activity of RFs in the superficial layers of the SC may be on average over 5 times greater than the RF area determined using conventional methods and criteria. These findings raise the interesting possibility that the relatively small size and sharp borders characteristic of RFs in the superficial layers arise from local inhibitory networks which delimit a broader field of excitatory activity supplied by retinal and cortical afferent terminals. Thus, in order to generate the RF changes observed here, either these local inhibitory circuits are amphetamine sensitive, or more likely, these inhibitory networks are dynamically modulated by an, as yet unidentified, amphetamine-sensitive input affecting visual RFs in the superficial layers.     

Effect of multiplicative noise on least-squares parameter estimation with applications to the atomic force microscope

Measurement of the power spectral density of (stochastic) Brownian fluctuations of micro- and nano-devices is used frequently to gain insight into their mechanistic properties. Noise is always present in these measurements and can directly influence any parameter estimation obtained through a least-squares analysis. Importantly, measurements of the spectral density of stationary random signals, such as Brownian motion, inherently contain multiplicative noise. In this article, we theoretically analyze the impact of multiplicative noise on fit parameters extracted using a least-squares analysis. A general analysis is presented that is valid for any fit function with any number of fit parameters. This yields closed-form expressions for the expected value and variance in the fit parameters and provides a rigorous theoretical framework for a priori determination of the effect of measurement uncertainty. The theory is demonstrated and validated through Monte Carlo simulation of synthetic data and by comparison to power spectral density measurements of the Brownian fluctuations of an atomic force microscope cantilever - analytical formulas for the uncertainty in the fitted resonant frequency and quality factor are presented. The results of this study demonstrate that precise measurements of fit parameters in the presence of noise are inherently problematic - individual measurements of the power spectral density are capable of yielding fit parameters that are many standard deviations away from the mean, with finite probability. This is of direct relevance to a host of applications in measurement science, including those connected with the atomic force microscope.     

Experimental testing of ductile cladding connections for building facades

A ductile cladding connection is a special connecting device between a facade cladding panel and a building structure that is designed to dissipate energy when subjected to an earthquake. The effect of such a device is to reduce the overall seismic response of the structure. A special testing machine was designed to test the behavior of these advanced cladding connections. The machine, which is specially suited for the recording and evaluation of ductility and damping properties, is described. Its main characteristics are both the ability to load a specimen in shear simultaneously in two orthogonal directions without inducing any axial stress, and the flexibility to test a wide variety of different damping mechanisms with different geometric configurations. The machine was used to test a family of advanced cladding connections that employs ductile flexural action to achieve high and stable levels of ductility for repeated cyclic load applications. A lumped-parameter mechanical model for these connections was identified from selected test data, and the predicted cyclic behavior was shown to agree well with test data. The model is simple and suitable for incorporation into nonlinear structural analysis programs.     

Light extinction by fine atmospheric particles in the White Mountains region of New Hampshire and its relationship to air mass transport

Chemical, optical, and physical measurements of fine aerosols (aerodynamic diameter < or = 2.5 microm) have been performed at a mountaintop location adjacent to the White Mountain National Forest in northern NH, USA. A 1-month long sampling campaign was conducted at Cranmore Mountain during spring 2000. We report on the apportionment of light extinction by fine aerosols into its major chemical components, and relationships between variations in aerosol parameters and changes in air mass origin. Filter-based, 24-h integrated samples were collected and analyzed for major inorganic ions, as well as organic (OC), elemental (EC), and total carbon. Light scattering and light absorption coefficients were measured at 5-min intervals using an integrating nephelometer and a light absorption photometer. Fine particle number density was measured with a condensation particle counter. Air mass origins and transport patterns were investigated through the use of 3-day backward trajectories and a synoptic climate classification system. Two distinct transport regimes were observed: (1) flow from the north/northeast (N/NE) occurred during 9 out of 18 sample-days; and (2) flow from the west/southwest (W/SW) occurred 8 out of 18 sample-days. All measured and derived aerosol and meteorological parameters were separated into two categories based on these different flow scenarios. During W/SW flow, higher values of aerosol chemical concentration, absorption and scattering coefficients, number density, and haziness were observed compared to N/NE flow. The highest level of haziness was associated with the climate classification Frontal Atlantic Return, which brought polluted air into the region from the mid-Atlantic corridor. Fine particle mass scattering efficiencies of (NH4)2SO4 and OC were 5.35 +/- 0.42 m2 g(-1) and 1.56 +/- 0.40 m2 g(-1), respectively, when transport was out of the N/NE. When transport was from the W/SW the values were 4.94 +/- 0.68 m2 g(-1) for (NH4)2SO4 and 2.18 +/- 0.91 m2 g(-1) for OC. EC mass absorption efficiency when transport was from the N/NE was 9.66 +/- 1.06 m2 g(-1) and 10.80 +/- 1.76 m2 g(-1) when transport was from the W/SW. Results from this work can be used to predict visual air quality in the White Mountain National Forest based on a forecasted synoptic climate classification and its associated visibility.     

Static and dynamic performance degradation of CMOS buffers due to ionizing radiation

It has been known for some time that ionizing radiation has profound effects on integrated circuits. These need to be considered when such devices may be subjected to radiation environments, such as in the space and nuclear industries. As even the space industry is making increased use of commercial off-the-shelf components for cost considerations, it is again becoming more important to characterize the degradation profiles of ICs which have not necessarily been radiation hardened. To that effect, the performance characteristics as functions of total dose have been analyzed for Motorola MC14050B CMOS Hex buffers in order to identify some relevant parameters. This paper presents the static (dc) and dynamic (ac) characteristics of these devices which have been subjected to increasing total doses under different bias conditions.     

Is contact lens "T" still important?

We studied oxygen supply to the contact lens covered cornea by means of a complex calculation method. We measured lens thicknesses, both centrally and at a 3mm peripheral location, of a range of optical powers of two different spherical silicone hydrogel contact lens designs (manufactured by Ciba Vision and Bausch & Lomb) and one "traditional" hydrogel. Using the measured values of lens thickness and the nominal oxygen permeabilities of these three plastics, we calculated the oxygen tension level in the tear layer posterior to the contact lens and anterior to the cornea and the oxygen flux through these contact lenses, under both open- and closed-eye conditions. We conclude that variable thicknesses of the silicone hydrogel contact lenses does not significantly affect the oxygen tension in the entrapped tear layer, given their high oxygen diffusion coefficients, under open-eye conditions, and probably only minimally under closed-eye conditions as well.