Timing for the absence of a stimulus: The gap paradigm reversed.

Contrary to data showing sensitivity to nontemporal properties of timed signals, current theories of interval timing assume that animals can use the presence or absence of a signal as equally valid cues as long as duration is the most predictive feature. Consequently, the authors examined rats' behavior when timing the absence of a visual or auditory stimulus in trace conditioning and in a "reversed" gap procedure. Memory for timing was tested by presenting the stimulus as a reversed gap into its timed absence. Results suggest that in trace conditioning (Experiment 1), rats time for the absence of a stimulus by using its offset as a time marker. As in the standard gap procedure, the insertion of a reversed gap was expected to "stop" rats' internal clock. In contrast, a reversed gap of 1, 5-, or 15-s duration "reset" the timing process in both trace conditioning (Experiment 2) and the reversed gap procedure (Experiment 3). A direct comparison of the standard and reversed gap procedures (Experiment 4) supported these findings. Results suggest that attentional mechanisms involving the salience or content of the gap might contribute to the response rule adopted in a gap procedure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of electromigration effects within various types of aluminum test structures

Advances in integrated circuit fabrication technology over the past two decades have resulted in integrated circuits with smaller device dimensions and larger area and complexity. This evolution of technology highlights electromigration as a major reliability problem in silicon VLSI circuits. Emphasis is placed on the scope and detail of the electromigration test structures themselves, and on the analysis of electromigration effects within various types of aluminum test structures.     

Study of photoconductivity in thin amorphous diamond-like carbon (a:DLC) films prepared by r.f. glow discharge technique

Thin a:DLC films were deposited by r.f. plasma system in which methane (CH₄) was admitted. Photoconductivity measurements were performed on an Al-a:DLC-Cu sandwich structure and an Al-a:DLC-Al planar structure. The photocurrent was measured in a wide interval of temperatures. The photocurrent signal of the sandwich device is about 100 times higher than the dark current measured under He-Ne laser incident light (2.5 mW) at 160 K. A photocurrent response time of τ_o ≈ 8 ms was measured at this temperature. In the planar device, under the same conditions, the photocurrent signal was twice the dark current. The maximum mobility-lifetime product of a:DLC (sandwich device) was about 2 × 10⁻¹⁰ cm²/V.     

The effect of processing parameters on the bond strength and electrical conductivity of multi-wall carbon nanotube/low-density polyethylene composite

The objective of this paper is to study the influence of processing parameters, such as melt temperature and mold temperature, on the adhesion of low density polyethylene (LDPE) to 2.5?wt/% multi-wall carbon nanotube-filled polyethylene (LDPE/MWCNT). The adhesion was obtained using two-component injection-molding method and measured using tensile experiments. The electrical conductivity of the two-component injection-molded specimens was also measured through DC voltage and compared to the volume resistivity of the LDPE and LDPE/MWCNT composite. It was found that the bond strength increases with increasing melt and mold temperatures. However, increasing the melt and mold temperatures over a certain limit can decrease the bond strength. The range of the electrical conductivity of the LDPE-LDPE/MWCNT two-component injection-molded samples was in the range of dissipative materials.     

Tolerance to chronic delta-9-tetrahydrocannabinol (Δ?-THC) in rhesus macaques infected with simian immunodeficiency virus.

Although Δ?-THC has been approved to treat anorexia and weight loss associated with AIDS, it may also reduce well-being by disrupting complex behavioral processes or enhancing HIV replication. To investigate these possibilities, four groups of male rhesus macaques were trained to respond under an operant acquisition and performance procedure, and administered vehicle or Δ?-THC before and after inoculation with simian immunodeficiency virus (SIVmac251, 100 TCID??/ml, i.v.). Prior to chronic Δ?-THC and SIV inoculation, 0.032–0.32 mg/kg of Δ?-THC produced dose-dependent rate-decreasing effects and small, sporadic error-increasing effects in the acquisition and performance components in each subject. Following 28 days of chronic Δ?-THC (0.32 mg/kg, i.m.) or vehicle twice daily, delta-9-THC-treated subjects developed tolerance to the rate-decreasing effects, and this tolerance was maintained during the initial 7–12 months irrespective of SIV infection (i.e., +THC/?SIV, +THC/+SIV). Full necropsy was performed on all SIV subjects an average of 329 days post-SIV inoculation, with postmortem histopathology suggestive of a reduced frequency of CNS pathology as well as opportunistic infections in delta-9-THC-treated subjects. Chronic Δ?-THC also significantly reduced CB-1 and CB-2 receptor levels in the hippocampus, attenuated the expression of a proinflammatory cytokine (MCP-1), and did not increase viral load in plasma, cerebrospinal fluid, or brain tissue compared to vehicle-treated subjects with SIV. Together, these data indicate that chronic Δ?-THC produces tolerance to its behaviorally disruptive effects on complex tasks while not adversely affecting viral load or other markers of disease progression during the early stages of infection. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Flow regimes in trickle beds using magnetic emulation of micro/macrogravity

Strong inhomogeneous magnetic fields in atmospheric-bore superconducting solenoid magnets were used to investigate the hydrodynamics in bore-fitted trickle beds which undergo emulated earth-bound artificial micro/macrogravity. This environment was able to modify the apparent gravity for both diamagnetic and paramagnetic materials by means of magnetization body force densities. Body force vectors can be co-linear or antiparallel to the cocurrent two-phase downflow in trickle beds depending on material magnetic susceptibilities, magnetic field gradient and direction of magnetic field. Trickle-to-pulse flow transition was experimentally studied in microgravity, macrogravity and beyond-levitation conditions for the air-water and the phenylacetylene-kerosene/hydrogen systems. Magnetic fields were found to displace the transition boundary from trickle to pulse flow. This was rationalized in terms of an equivalent artificial gravity effect by formally commuting magnetization forces into an equivalent gravitational acceleration. A theoretical analysis, using a modified Grosser et al. [1988. Onset of pulsing in two-phase cocurrent downflow through a packed bed. A.I.Ch.E. Journal 34, 1850-1860] “artificial gravity” transition model, was carried out and model predictions were found to follow qualitatively the experimental findings.     

Optimization and design of alkaline pulping of rapeseed (Brassica napus) stalks

Rapeseed (Brassica napus) stalks are agricultural wastes generated in important quantities as a result of rapeseed cultivation valued for edible vegetable oil or biodiesel production. This study examines the potential of using rapeseed stalks as raw material in pulp production. The obtained results pointed out to the suitability of these agricultural wastes for pulping to papermaking pulp. Chemical alkaline pulping methods such as kraft and sulphur-free soda-anthraquinone and their optimization were taken into consideration for the laboratory trials. Response surface modeling was employed for the study of process parameters impact on obtained pulps. As a result, optimal process conditions may be selected depending on the desired pulp characteristics.