Functional brain imaging using EPI at 3 T

Functional magnetic resonance imaging (fMRI) is becoming an important tool in the mapping of brain activation. However there are two main concerns that need to be answered before functional imaging can be considered truly useful as a neurophysiological tool. The first is that the detected activation may be derived from large veins and, thus, be spatially separate from the underlying brain activity. The second is the incomplete understanding of the brain transfer function and its relation to brain activity, blood flow, and metabolism. This work contains initial results that will help address these points. Models of the brain vasculature predict that signal changes on SE (spin-echo) images are expected to be much smaller in magnitude but very accurate in localizing true areas of activation than on GE (gradient-echo) images which are susceptable to large veins. By comparing activation from SE and GE EPI at 3 T, we have shown that the regions of activation are spatially very similar, suggesting that GE activation is closely linked to the underlying brain activity. We have identified an experimental impulse response of the brain following 8-s visual stimulation. This impulse response can be used to successfully predict the frequency response obtained experimentally and its shape suggests a resonance phenomenon. This suggests the brain transfer function can be modeled from linear response theory corresponding to the inherent feedback control mechanisms of the brain homeostasis. Continuation of this early work will help to identify the links between fMRI signal change and underlying brain physiology.     

The feedback adaptive line enhancer: a constrained IIR adaptivefilter

A new adaptive line enhancer (ALE) structure, called the Feedback ALE (FALE), is presented and is shown to be a constrained W adaptive filter. Extensive simulations show that the FALE gives a higher sine-to-broadband ratio (SBR) gain and smaller sine estimation error than does an equal-order ALE; conversely, the order of the FALE can be much low er than the ALE to achieve equivalent performance     

A dynamic vector model of microstrip RF resonators for high-field MR imaging

This paper describes a dynamic vector model for modelling the electromagnetic characteristics of microstrip radio-frequency (RF) resonators for high field magnetic resonance imaging (MRI). A biological tissue-equivalent load having a circular cross section is assumed in the analysis. The dynamic model uses the well-known Green's function for cylindrically stratified media to characterize all six components of the electromagnetic field excited by the microstrip lines. The accuracy of the method as a function of its parameters is assessed and the results compared with those obtained from the quasi-static method often used at low frequencies. The limits of the quasi-static assumption are investigated by comparing values for the modal propagation constant and the terminating capacitances required to tune the cavity resonance over a frequency range of 100 MHz-1 GHz. The dynamic method is further used to analyse the modal content of a microstrip head resonator. Finally, a variational approach is used to assess the impact of the intermodal coupling for the case of small perturbations in the shape and the position of the cylindrical phantom.     

Life-cycle economic analysis of distributed manufacturing with open-source 3-D printers

The recent development of open-source 3-D printers makes scaling of distributed additive-based manufacturing of high-value objects technically feasible and offers the potential for widespread proliferation of mechatronics education and participation. These self-replicating rapid prototypers (RepRaps) can manufacture approximately half of their own parts from sequential fused deposition of polymer feedstocks. RepRaps have been demonstrated for conventional prototyping and engineering, customizing scientific equipment, and appropriate technology-related manufacturing for sustainable development. However, in order for this technology to proliferate like 2-D electronic printers have, it must be economically viable for a typical household. This study reports on the life-cycle economic analysis (LCEA) of RepRap technology for an average US household. A new low-cost RepRap is described and the costs of materials and time to construct it are quantified. The economic costs of a selection of 20 open-source printable designs (representing less than 0.02% of those available), are typical of products that a household might purchase, are quantified for print time, energy, and filament consumption and compared to low and high Internet market prices for similar products without shipping costs. The results show that even making the extremely conservative assumption that the household would only use the printer to make the selected 20 products a year the avoided purchase cost savings would range from about $300 to $2000/year. Assuming the 25 h of necessary printing for the selected products is evenly distributed throughout the year these savings provide a simple payback time for the RepRap in 4 months to 2 years and provide an ROI between >200% and >40%. As both upgrades and the components that are most likely to wear out in the RepRap can be printed and thus the lifetime of the distributing manufacturing can be substantially increased the unavoidable conclusion from this study is that the RepRap is an economically attractive investment for the average US household already. It appears clear that as RepRaps improve in reliability, continue to decline in cost and both the number and assumed utility of open-source designs continues growing exponentially, open-source 3-D printers will become a mass-market mechatronic device.     

Interaction of relativistic electrons with ultrashort laser pulses:generation of femtosecond X-rays and microprobing of electron beams

The interaction of relativistic electrons with terawatt femtosecond laser pulses is reviewed with emphasis on how the scattering process can be used as a source of ultrashort X-ray pulses and as a time-resolved diagnostic for measuring transverse and longitudinal phase space distributions of an electron beam with microns spatial and subpicosecond temporal resolution. Recent experimental results are presented in which 90° Thomson scattering was utilized to generate 300 fs duration pulses of X-rays with peak energy of 30 keV. It is shown that, through analysis of the scattered X-ray beam properties, transverse and longitudinal distributions of the electron beam can be obtained     

Addition of carbon black NIR absorber to galvanised steel primer systems: Influence on NIR cure of polyester melamine topcoats and corrosion protection characteristics

Near infrared (NIR) is becoming a popular option for rapid cure of coatings in the coil coating industry particularly where fast line speeds are required. The technology has the potential to reduce the cure time of a 20 μm polyester coating on a galvanised steel substrate from around 30 s via conventional heating methods down to <10 s under the lamps. Previous work suggested that the ideal situation in this case is to have a topcoat which is slightly transparent to NIR and an absorbing substrate to heat the coating from the substrate outwards in a two stage process which separates solvent removal from cross linking and film formation. This can be taken further by tinting the primer layer with a pigment that absorbs in the NIR region. In this study spectroscopy was used to show that a coated steel system could appear white in the visible region because of the reflectance of TiO₂ but the NIR absorption could be altered by adding absorbing pigments such as carbon black. Lamp settings could be reduced by 20% to achieve equivalent cure with tinted primer systems. The potential degradation in corrosion protection afforded by carbon-black containing pigments at various loadings was assessed for model organic coatings applied to galvanised steel specimens. In situ scanning Kelvin probe studies showed that rates of corrosion-driven coating delamination by cathodic disbondment remained unchanged by pigment loadings of up to 3.5 wt%.     

Comparative analysis of sex-pheromone-response antagonists in three races of European corn borer

Behavioral responses of males from three New York races of European corn borer,Ostrinia nubilalis (Hübner), to various suspected sexpheromone-response antagonists were investigated with a flight tunnel protocol. Males from a bivoltine (Z) race and from a univoltine (Z) race utilizing a natural pheromone blend of 982 (Z)-(E)-11-tetradecenyl acetates and males from a bivoltine (E) race utilizing a 199 (Z)-(E)-11-tetradecenyl acetate ratio were flown to their natural blends and to blends containing 1 % of one of the following additional compounds: Z9–12OAc,E9–12OAc,Z9–14OAc, andE9–14OAc. In each race, the added components lowered significantly the number of individuals completing the behavioral sequence. The only exception was bivoltineE males flown to a blend withE9–12OAc added. The number completing the sequence in this case was statistically not significantly lower than the number that completed the sequence to the standard blend. In all three races, theZ9–14OAc produced the most dramatic reduction in completed flights, and in the univoltineZ race, this added component was significantly more effective in reducing completed flights than any other added component. The response to the Z9–14OAc is understandable given recently published findings of an electrophysiological study of single sensilla in the European corn borer.     

The Role of Oxygen Storage in NO Conversion in Automotive Catalysts

An asymmetry in NO conversion efficiency is apparent during trans-stoichiometric air–fuel ratio steps over a three-way catalyst. After a lean-to-rich step, NO conversion becomes high very rapidly and asymptotes to a higher value, followed by a reduction to a high, but reduced level. Following a rich-to-lean step, conversion remains high for a period before gradually decreasing to the low level seen at steady lean operation. This dynamic response in NO conversion can be modelled by a three-way catalyst model which includes ceria reoxidation by way of NO dissociative adsorption. Five, periodic, different aspect triangular waveforms were tested to try to exploit the asymmetry by waveform shaping. No strong trends in average NO conversion efficiency resulted; however, some shapes seemed to give a better overall conversion.     

Breast disease: dynamic spiral MR imaging

The cochleo- and tonotopic organization of the second auditory area (AII) was investigated in cats anaesthetized with pentobarbital using a combination of macro- and microelectrode recording technique. The results obtained following electrical stimulation of the neural fibres innervating different regions of the organ of Corti indicate the existence of two complete representations of the cochlea in area AII: one in the dorsocaudal portion, the other in its ventrorostral portion. These two cortical representations of the cochlea differ in size and spatial orientation. The dorsocaudal projection area extends over a distance of 2.6-3.2 mm from the basal to the apical focus and is arc-shaped. The spatial orientation of cochlea representation within the dorsocaudal region of AII is similar to that described in AI, in that stimulation of the cochlea base results in maximal responses in the more rostral portion of AII and stimulation of the apex evokes cortical responses more caudally. The ventrorostral region within AII is smaller (1.4-2.5 mm length), and has the opposite cochleotopic orientation (base and apex stimulation represented caudally and rostrally, respectively). In both AII zones, there was a proportionally greater cortical representation of basilar membrane than of middle and apical portions. Although two distinct zones with the overall cochleotopic pattern described above were noted in all cats, their precise size and location considerably varied in different animals. Using microelectrode recordings, a cortical tonotopic organization can be observed that was consistent with and expanded on the earlier cochleotopic data. Within the dorsocaudal region of AII, neurons with higher best frequency responses were located in more rostral regions, while those with lower best frequencies were located caudally. An orderly progression of best frequency responses was noted as serial recordings carried out along the full extent of the representation. Neurons within the ventrorostral region of AII also displayed an orderly progression of best frequencies, but in the opposite direction, with higher best frequencies noted more caudally and lower best frequencies more rostrally.