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Optical brain imaging using functional near infra-red spectroscopy
(fNIRS) offers a portable and noninvasive tool for monitoring of blood oxygenation.
In this paper we have introduced a new miniaturized photodetector front-end on achip
to be applied in a portable fNIRS system. It includes silicon avalanche photodiodes
(SiAPD), Transimpedance amplifier (TIA) front-end and Quench-Reset circuitry to
operate in both linear and Geiger modes. So it can be applied for both continuous-wave
fNIRS (CW-fNIRS) and also single-photon counting. Proposed SiAPD exhibits high-avalanche
gain (>100), low-breakdown voltage (<12 V) and high photon detection
efficiency accompanying with low dark count rates. The proposed TIA front-end offer
a low power consumption (<1 mW), high-transimpedance gain (up to 250 MV/A), tunable
bandwidth (1 kHz - 1 GHz) and very low input and output noise (~few fA/√Hz and few μV/√Hz).
The Geiger-mode photon counting front-end also exhibits a controllable hold-off
and rest time with an ultra fast quench-reset time (few ns). This integrated system
has been implemented using submicron (0.35 μm) standard CMOS technology.
The emerging field of neuroprosthetics is focused on design and implementation of neural prostheses to restore some of the lost neural functions. Remarkable progress has been reported at most bioelectronic levels—particularly the various brain-machine interfaces (BMIs)—but the electrode-tissue contacts (ETCs) remain one of the major obstacles. The success of these BMIs relies on electrodes which are in contact with the neural tissue. Biological response to chronic implantation of Microelectrode arrays (MEAs) is an essential factor in determining a successful electrode design. By altering the material compositions and geometries of the arrays, fabrication techniques of MEAs insuring these ETCs try to obtain consistent recording signals from small groups of neurons without losing microstimulation capabilities, while maintaining low-impedance pathways for charge injection, high-charge transfer, and high-spatial resolution in recent years. So far, none of these attempts have led to a major breakthrough. Clearly, much work still needs to be done to accept a standard model of MEAs for clinical purposes. In this paper, we review different microfabrication techniques of MEAs with their advantages and drawbacks, and comment on various coating materials to enhance electrode performance. Then, we propose high-density, three-dimensional (3D), silicon-based MEAs using micromachining methods. The geometries that will be used include arrays of penetrating variable-height probes.
This study investigates the statistical
relationship between climatic variables and aspects of cotton production (G.
barbadense), and the effects of climatic factors prevailing prior to flowering or subsequent to boll setting on flower and boll production and retention
in cotton. The effects of specific climatic factors during both pre- and
post-anthesis periods on boll production and retention are mostly unknown.
However, by determining the relationship of climatic factors with flower and
boll production and retention, the overall level of production can be possibly
predicted. Thus, an understanding of these relationships may help
physiologists determine control mechanisms of production in cotton plants.
Also, the study covers the predicted effects of climatic factors during
convenient intervals (in days) on cotton flower and boll production
compared with daily observations. Further, cotton flower and boll production
as affected by climatic factors and soil moisture status has been considered.
Evaporation, sunshine duration, relative humidity, surface soil temperature
at 1800 h, and maximum air temperature, are the important climatic factors
that significantly affect flower and boll production. The least important
variables were found to be surface soil temperature at 600 h and minimum
temperature. The five-day interval was found to be more adequately and sensibly
related to yield parameters. Evaporation, minimum humidity and sunshine
duration were the most effective climatic factors during preceding and succeeding periods on boll production and retention. There was a negative correlation
between flower number and boll production and either evaporation or sunshine
duration, while that correlation
with minimum relative
humidity was positive. The soil moisture status showed low and insignificant
correlation with flower and boll production. Higher minimum relative
humidity, short period of sunshine duration, and low temperatures enhanced
flower and boll formation.