Fractal community tissue: Differentiating the energy harvest through self-similar urban form

This paper describes the application of fractal dimensioning and self-similar geometric patterning properties to the strategic harvest of solar energy. Specifically, the paper examines application of fractal principles at the scales of community, building, component, and material surface. Using fundamental geometric properties as the “simple rules applied repeatedly”, one can maximize (at differing scales) the opportunity for differentiating and managing the energy harvest to fit user(s) need. The paper discusses the use of fractal patterning as a means of dimensioning and scaling the “ratios of transparency” — the formal geometric expressions of conversion potential resulting from surface roughness condition(s). Roughness in fractal terms is a relative factor ranging in application from community-scale constructs on the land (which can mimic natural physiography) to the microscopic geometry of PV semi-conductor surfaces. Specific illustration at the scales cited can be correlated to the spreadsheet inventorying of energy harvest potentials. Fractal patterning provides an opportunity for treating strategies of energy harvest — embodied in community, building, component, and material surface — as seeds for a new urban form.     

Laterally scaled Si-Si/sub 0.7/Ge/sub 0.3/ n-MODFETs with f/sub max/>200 GHz and low operating bias

We report on the dc and RF characterization of laterally scaled, Si-SiGe n-MODFETs. Devices with gate length, L/sub g/, of 80 nm had f/sub T/=79 GHz and f/sub max/=212 GHz, while devices with L/sub g/=70 nm had f/sub T/ as high as 92 GHz. The MODFETs displayed enhanced f/sub T/ at reduced drain-to-source voltage, V/sub ds/, compared to Si MOSFETs with similar f/sub T/ at high V/sub ds/.     

Studies on the anchorage of ATP diphosphohydrolase in synaptic plasma membranes from rat brain

We examined performance in young and elderly on an implicit (lexical decision) and an explicit (recognition) memory test. The difference in lexical decision times between old and new words was equivalent in the two groups, although the elderly were slower. In both groups, recognition accuracy (lower in the elderly) was higher following semantic than nonsemantic encoding, whereas lexical decision times were unaffected. Divergent brain potentials for old and new words during lexical decisions constituted a repetition effect, which reflected greater positivity (200-800 ms) for old words, particularly over the left hemisphere; this effect was smaller and later in the elderly. An electrophysiological marker of enhanced recollection for words from the semantic encoding task took the form of a left-sided positivity (500-800 ms). The effect was smaller in the elderly than the young, providing an additional index of their impaired recognition processes.     

Calcium dynamics in single spines during coincident pre- and postsynaptic activity depend on relative timing of back-propagating action potentials and subthreshold excitatory postsynaptic potentials

We compared the transient increase of Ca2+ in single spines on basal dendrites of rat neocortical layer 5 pyramidal neurons evoked by subthreshold excitatory postsynaptic potentials (EPSPs) and back-propagating action potentials (APs) by using calcium fluorescence imaging. AP-evoked Ca2+ transients were detected in both the spines and in the adjacent dendritic shaft, whereas Ca2+ transients evoked by single EPSPs were largely restricted to a single active spine head. Calcium transients elicited in the active spines by a single AP or EPSP, in spines up to 80 micro(m) for the soma, were of comparable amplitude. The Ca2+ transient in an active spine evoked by pairing an EPSP and a back-propagating AP separated by a time interval of 50 ms was larger if the AP followed the EPSP than if it preceded it. This difference reflected supra- and sublinear summation of Ca2+ transients, respectively. A comparable dependence of spinous Ca2+ transients on relative timing was observed also when short bursts of APs and EPSPs were paired. These results indicate that the amplitude of the spinous Ca2+ transients during coincident pre- and postsynaptic activity depended critically on the relative order of subthreshold EPSPs and back-propagating APs. Thus, in neocortical neurons the amplitude of spinous Ca2+ transients could encode small time differences between pre- and postsynaptic activity.     

MEMS: small machines for the microelectronics age

In the past few years, the micro-electromechanical systems (MEMS) industry has exceeded the $1-billion-a-year mark. Some economic forecasters estimate that the industry will surpass $14 billion by the year 2000. The reason for this tremendous growth is the enabling nature of MEMS, which give engineers and researchers the tools to build things that have been impossible or prohibitively expensive with other techniques. MEMS are micron- to millimeter-scale devices that can be fabricated as discrete devices or in large arrays. MEMS borrow much of their technology from integrated circuit (IC) manufacturing, providing three-fold benefits: miniaturization, multiplicity and microelectronics. First, miniaturization of the devices is inherent in the processing techniques. Modern microelectronics fabrication techniques are designed to build submicron-scale devices. By using the same techniques, engineers can easily leverage this technology to produce MEMS that are orders of magnitude smaller than their macroworld counterparts. Second, the use of photolithography techniques makes producing thousands or even millions of copies of a single device easy. Thus, single devices can be arrayed into systems to produce an effect impossible with discrete devices. Finally, because MEMS technology is so similar to IC fabrication technology, MEMS are integrable with microelectronics     

Operation of a novel negative differential conductance transistorfabricated in a strained Si quantum well

The operation of a negative differential conductance (NDC) transistor fabricated on a high-mobility Si/Si_1-xGe_x heterostructure wafer is described. The drain characteristic of this device shows a large NDC with current peak-to-valley ratios as high as 600 (100) at T=0.4 K (T=1.3 K). The NDC can be modulated over a wide range of current levels by either of two separately-contacted gate electrodes. The device shows bistable switching behaviour in both current- and voltage-controlled circuit configurations. The novel operating principle of this transistor is described, along with its potential for future logic and memory applications     

Undoped-Body Extremely Thin SOI MOSFETs With Back Gates

We present a detailed study of gate length scalability and device performance of undoped-body extremely thin silicon-on-insulator (ETSOI) MOSFETs with back gates. We show that short channel control improves with the application of back bias via a decrease in the electrostatic scaling length as the subthreshold charges move toward the front gate. We demonstrate that, even for undoped ETSOI devices with ~8-nm SOI thickness, the improvement in short channel control with the application of a back bias translates to 10% higher drive current, 10% shorter gate lengths, and, consequently, 20% lower extrinsic gate delay at a fixed off-state current of 100 nA/mum and a back oxide electric field of 1.5 MV/cm (0.5 MV/cm SOI field).     

Ofloxacin/beta-cyclodextrin complexation

Ofloxacin (OFX) is a fluorquinolone characterized by photochemical instability. With the goal to improve its photostability in aqueous solutions, the complexation of ofloxacin with β-cyclodextrin was investigated. The complexes showed a water solubility enhancement of approximately 2.6 times; nevertheless, the photodegradation of ofloxacin was not reduced. The complexes obtained were characterized by thermal and ¹H nuclear magnetic resonance (NMR) analysis, which revealed an interaction between ofloxacin and β-cyclodextrin. The last analysis indicated that only partial inclusion of the N-methylpiperazinyl moiety occurred, which can explain the fact that photostabilization was not improved. This partial inclusion phenomenon could be explained also by computer-aided molecular modeling.