Reduced Power Requirements Research Articles

Microcavity Laser Oscillating in a Circuit-Based Resonator

Lasers based on microcavities are extremely attractive for their compactness, low power dissipation, and potential for ultrafast modulation speed. We describe an ultrasmall laser based on a subwavelength electronic inductor-capacitor (LC) resonant circuit that allows for extreme confinement of the electric field. This electrically injected laser operates at a frequency of 1.5 terahertz, and the mode volume is strongly subwavelength. The design concept of the LC resonator can be extended from the terahertz range to higher frequencies and also applied to detectors and modulators.

Effect of tillage system and straw management on organic matter dynamics

The choice of cultivation system in arable agriculture exerts a strong influence not only on soil health and crop productivity but also on the wider environment. Conservation tillage using non-inversion methods conserves soil carbon, reduces erosion risk and enhances soil quality. In addition, conservation tillage has been shown to sequester more carbon within the soil than inversion tillage, reducing carbon dioxide losses to the atmosphere. Stable, well structured topsoils that develop following long-term conservation tillage lead to more energy efficient systems due to the reduced power requirements for cultivation. Long-term experiments, e.g. more than 20 years, that confirm the impact of conservation tillage over an extended period are not common. Here we evaluate the impact of different tillage methods and winter wheat straw management, either incorporated or removed, on organic matter turnover and soil quality indicators. No-till, chisel and mouldboard ploughing was carried out for 23 years on a silty clay loam soil in South West England that was not considered suitable for non-inversion tillage due to weak soil structure. In order to assess the effect of contrasting cultivation and straw disposal method on soil carbon dynamics, a range of assays were conducted, including water extractable organic carbon, hot water extractable carbohydrate, microbial biomass carbon, activity of β-glucosidase and acid phosphatase enzymes, C sequestration and the natural abundance of 13C. Our results show that the soil organic carbon concentration in the topsoil was greater under no-till than mouldboard ploughing, while a reverse trend was observed in the lower depths. A 14–17% increase in soil organic carbon was observed in the topsoil for chisel plough and no-till treatments compared to mouldboard ploughing. Water extractable organic carbon was found to constitute only 1–7% of the microbial biomass carbon. Hot water extractable carbohydrate was one of the most sensitive indicators of soil quality and had a significant a negative correlation with bulk density and positive correlation with soil organic carbon microbial biomass carbon β-glucosidase and acid phosphatase. The choice of cultivation method exerted a major control on microbial and carbon dynamics. No-till and chisel ploughing maintained carbon in the soil surface horizons, which will benefit the stability of this weakly structured soil, but mouldboard ploughing distributed carbon more uniformly throughout the soil profile, particularly when straw was incorporated, hence leading to the retention of more carbon in the soil profile.

High Throughput Parallel Decoding Method for H.264/AVC CAVLC

A high throughput parallel decoding method is developed for context-based adaptive variable length codes. In this paper, several new design ideas are devised and implemented for scalable parallel processing, a reduction in area, and a reduction in power requirements. First, simplified logical operations instead of memory lookups are used for parallel processing. Second, the codes are grouped based on their lengths for efficient logical operation. Third, up to M bits of the input stream can be analyzed simultaneously. For comparison, we designed a logical-operation-based parallel decoder for M=8 and a conventional parallel decoder. High-speed parallel decoding becomes possible with our method. In addition, for similar decoding rates (1.57 codes/cycle for M=8), our new approach uses 46% less chip area than the conventional method.

Inexpensive, universal serial bus-powered and fully portable lab-on-a-chip-based capillary electrophoresis instrument

Capillary electrophoresis is a cornerstone of lab-on-a-chip (LOC) implementations for medical diagnostics. However, the infrastructure needed to operate electrophoretic LOC implementations tends to be large and expensive, hindering the development of portable or low-cost systems. A custom-designed and highly integrated microelectronic chip for high-voltage generation switching and interfacing is recently developed. Here, the authors integrate the microelectronic chip with a microfluidic chip, a solid-state laser, filter, lens and several dollars worth of electronic components to form an inexpensive and portable platform, which is the size of a mobile telephone. This compact system has such reduced power requirements that the complete platform can be operated using a universal serial bus link to a computer. It is believed that this system represents a significant advancement in practical LOC implementations for point-of-care medical diagnostics.

Optimization of intercooling compression in CO 2 capture systems

Compression of CO 2 is an essential process in the development of carbon capture and storage (CCS) technologies. In spite of power requirements for CO 2 compression could be as much as 100 kWe per tonne CO 2, the minimization of energy requirements has received little attention in the literature. Although intercooling compression reduces power requirements, it introduces important cooling necessities that could be minimized. The aim of this paper is the integration of intercooling compression into the low-pressure part of a steam cycle to take advantage of the intercooling heat and analyse the energetic and economical results under different assumptions. Simulation and optimization have been performed in order to evaluate the intercooling configuration, energy requirements and the most cost-effective integration. Results have shown reduction in compression power requirement around 40% and reduction of the incremental COE around 23%. Proposed integration could be used to increase the efficiency of CO 2 capture processes and, therefore, to reduce the CO 2 capture cost.

Multi-axis Semi-active Vibration Control using Magnetorheological Technology

Parallel platform mechanisms with six degrees-of-freedom (DOF) are ideal candidates for precision positioning applications. Many of the precision positioning applications are located in environments where multi degrees of vibrations exist. From a design perspective, it will be logical to have a parallel platform mechanism, which is inherently an ideal mechanism for precise positioning, to provide vibration isolation at the same time. While passive vibration control and active vibration control have been extensively used in parallel platforms, a six DOF parallel platform which uses semi-active vibration control has not received as much attention. Advantages of semi-active control include reduced cost (by using a simpler actuator intended for only positioning), reduced power requirements, and improved stability. Within this work a six DOF parallel platform model is created. Each leg of the platform is modeled as a two DOF system with a coil-over magnetorheological (MR) damper for adjustable damping in series with an actuator used for positioning. The vibration isolation performance of the parallel platform mechanism and its positioning capability are quantified through simulations. Simulation results show that MR dampers are effective in six DOF vibration isolation applications when they are incorporated into parallel platform mechanisms.

VAZÕES ESPECÍFICAS MÍNIMAS PARA SECAGEM DO MILHO COM AR NATURAL EM BOTUCATU-SP

Minimum airflow rates are recommended to ambient air grain drying to reduce fan power requirements and grain overdrying. Historical weather records from 1971 were selected to determine airflow rates for drying corn with ambient air in Botucatu, Sao Paulo State. 1971 was the poorest drying year in the 10-year period from 1971 through 1975 and l977 through 1981. In the simulation of ambient air corn drying initial moisture contents, wet basis used were 22%, 20% and 18% within allowable storage periods of 7, 11 and 29 days, respectively, for monthly average dry bulb temperature of 23.40C, the upmost in the 10-year period. The average dry bulb temperature and relative humidity were calculated from the hourly data recorded at the Faculdade de Ciencias Agronomicas, Botucatu county, Sao Paulo State, weather station. Due to impracticable continuous drying occurrence, only selective ambient air drying was considered, within daily periods from 9 a. m. to 5 p.m., 9 a. am. to 6 p.m. and 8 a.m. to 6 p.m. The simulation results showed that the minimum airflow rates decrease rapidly with decreasing grain equilibrium moisture content a few percentage points. Furthermore, the reduction in daily fan operation a few hours requires significant increases in minimum airflow rates to accomplish ambient air corn drying within the permissible storage time.

Front-end electronics and trigger systems—Status and challenges

The past quarter century has brought about a revolution in front-end electronics for large-scale detector systems. Custom integrated circuits specifically tailored to the requirements of large detector systems have provided unprecedented performance and enabled systems that once were deemed impossible. The evolution of integrated circuit readouts in strip detectors is summarized, the present status described, and challenges posed by the sLHC and ILC are discussed. Performance requirements increase, but key considerations remain as in the past: power dissipation, material, and services. Smaller CMOS feature sizes will not reduce the power required for the desired noise levels, but will improve digital power efficiency. Significant improvements appear to be practical in more efficient power distribution. Enhanced digital electronics have provided powerful trigger processors that greatly improve the trigger efficiency. In data readout systems, they also improve data throughput, while reducing power requirements. Concurrently with new developments in high energy physics, detector systems for cosmology and astrophysics have made great strides. As an example, a large-scale readout for superconducting bolometer arrays is described.

Satellite Constellations for Continuous and Early Warning Observation: A Correlation-Based Approach

Recently, telecommunication and navigation corporations have shown a growing interest in low and medium Earth orbit constellations due to several operational advantages, such as reduced power requirements and signal time delays with respect to geostationary platforms. An increased imaging resolution of Earth's surface is also associated with the use of low orbits rather than high altitude orbits. A large set of parameters is involved in defining constellation configurations, so usually some basic assumptions are taken. For instance, this occurs for Walker constellations, exhibiting a high degree of symmetry and suitability for coverage of large areas. Yet, for special purposes, such as continuous observation or early warning monitoring of a specific location, geometric hypotheses often seem inadequate or oversimplified. In this paper all satellites are placed in circular, repeating orbits with semimajor axis and inclination yielding maximum visibility of a preselected target location. Then, a correlation function is introduced as an effective tool to find all allowed time delays between two consecutive passes over the target. Some optimal constellation configurations (of 2, 4, 8 satellites) are deduced and discussed with reference to different kinds of local observation.

Optimal control of a pretwisted shearable smart composite rotating beam

The optimal vibration control of a rotating, composite, pretwisted, single-celled box beam, exhibiting transverse shear flexibility and restrained warping, is analyzed. A higher-order shear deformation theory (HSDT) enabling satisfaction of traction-free boundary conditions is employed. An orthotropic host with Circumferentially Uniform Stiffness ply angle configuration and transversely isotropic sensors-actuator pairs that are surface embedded along the span are considered. The total output from sensors is fed to a controller and then uniformly applied to actuators. The extended Galerkin method, along with either instantaneous or classical LQR methods, is used. Instantaneous LQR provides greater response attenuation in case of sustained external forcing. Results are obtained for a linear spanwise variation of pretwist. Compared to the unshearable and first-order shearable (FSDT) models, the HSDT appears most sensitive to pretwist and – when a saturation constraint is considered – it predicts the lowest settling time. The HSDT predicts significant attenuation in response and power required as compared to the FSDT, the differences being especially pronounced for constrained input control. Parametric studies involving the ply angle, pretwist, and patch length are performed. An optimum pretwist that yields lowest response, power, and settling time is obtained. Its value differs when the saturation constraint is used. Tailoring provides greater attenuation at the expense of an increase in settling time. Using constrained input control, an order-of-magnitude reduction in power requirement is possible via tailoring. The results underscore the importance of shear strain variation across the beam wall, and also of synthesizing active control with tailoring, for achieving efficient control.

Autonomous Sensing and Control of Wing Stall Using a Smart Plasma Slat

DOI: 10.2514/1.24057 The concept of a self-governing smart plasma slat for active sense and control of flow separation and incipient wing stall is presented. The smart plasma slat design involves the use of an aerodynamic plasma actuator on the leading edge of a two-dimensional NACA 0015 airfoil in a manner that mimics the effect of a movable leading-edge slat of a conventional high-lift system. The self-governing system uses a single high-bandwidth pressure sensor and a feedback controller to operate the actuator in an autonomous mode with a primary function to sense and control incipient flow separation at the wing leading edge and to delay incipient stall. Two feedback control techniques are investigated. Wind tunnel experiments demonstrate that the aerodynamic effects of a smart actuator are consistent with the previously tested open-loop actuator, in that stall hysteresis is eliminated, stall angle is delayed by 7 deg, and a significant improvement in the lift-to-drag ratio is achieved over a wide range of angles of attack. These feedback control approaches provide a means to further reduce power requirements for an unsteady plasma actuator for practical air vehicle applications. The smart plasma slat concept is well suited for the design of low-drag, quiet, highlift systems for fixed-wing aircraft and rotorcraft.

Polymer-Based Ion Trap Chemical Sensor

Ion traps are widely used in chemical analysis, and they are especially important in current attempts to miniaturize mass spectrometers to create portable instruments. The ultimate aim is to build a handheld device that would require a smaller mass analyzer. To accomplish this task, a robust precision fabrication procedure is desired. In this paper, the authors report a new approach to fabricating ion traps using stereolithography apparatus (SLA), which provides precision monolithic fabrication. An SLA-fabricated rectilinear ion trap, which employs a very simple electrode geometry, is shown to provide detection capabilities within a useful mass range encompassing that of interest in the detection of numerous volatile organic compounds, including those relevant to homeland security applications. Single small ion traps and integrated trap arrays can be made through this approach, which allows higher operating pressures and reduced power requirements

Bluetooth Inquiry Time Characterization and Selection

The Bluetooth discovery process requires use of the inquiry substate which not only consumes significant power, but prevents normal data traffic flow and simultaneously acts as a potential noise source for neighboring networks. Therefore, the inquiry substate dwell time should be limited to discovering an acceptable number of neighboring devices. Although an estimate of the probability density function of the time to discover scanning devices is straightforward, the complex temporal and spectral interactions between two devices make precise inquiry time characterization difficult. We characterize these interactions and derive detailed analytical expressions for the probability distribution of the inquiry time for a Bluetooth-enabled device that follows v1.1 of the Bluetooth specification and uses the default 11.25 ms inquiry scan window that opens every 1.28 s. Subsequently, we show a single inquirer will locate 99 percent of all scanning devices within transmission range in 5.12 seconds rather than the 10.24 s recommended in the specification. Using specification v1.2, we show that the inquiry time can be reduced to 3.84 seconds and 1.28 seconds using the standard and interlaced inquiry scan modes, respectively. Substantial inquiry time reduction results in reduced power requirements and increased throughput by increasing data traffic and reducing interference with neighboring piconets. Our results are validated via comparison with existing simulation models and measurement studies. The models used to derive the distribution also lend themselves to characterizing the discovery time with variations in the discovery process

Comparison of Biofouling Control in a Membrane Bioreactor via Two Coarse Bubble Aeration Cycles

In the membrane bioreactor (MBR) process, coarse bubble aeration is used to scour the surface of the membranes to help control biofouling. Energy required for coarse bubble aeration represents a significant fraction of the total power demand for these systems. To reduce this demand, MBR systems manufactured by Zenon Environmental Inc. operate with cyclic aeration, using a cycle of 10 seconds on and 10 seconds off (10/10 aeration cycle). The objective of this study was to evaluate the potential to reduce power requirements for a full-scale Zenon MBR facility that is currently under construction by application of an alternative aeration cycle. The alternative cycle consists of 10 seconds on and 30 seconds off (10/30 aeration cycle), which reduces scouring air requirements by 50% from the 10/10 cycle. To achieve this objective, a pilot-scale evaluation using an existing 30-gallon per minute MBR plant was conducted. The specific goal of the evaluation was to compare the ability of the 10/10 and 10/30 cycles to control biofouling while operating over a range of flux values. In addition to the pilot-scale testing, an estimate of anticipated power costs savings resulting from implementation of the 10/30 cycle was determined for the full-scale facility. Key findings include: (1) While operating with the 10/10 cycle at a flux of 12 gallons/ft 2 -d (gfd) over a period of two months, there was no measurable fouling observed. The fouling rates at 15 and 18 gfd were approximately 0.1 and 0.3 psi/day, respectively; (2) While operating with the 10/30 cycle at 12 gfd, a relatively significant amount of fouling was observed after only 14 days of operation, indicating that long operating periods could not be sustained between membrane cleanings; (3) 10/30 cycle fouling, at a flux of 12 gfd, was significantly reduced by modifying the permeate production cycle of the system from 12 minutes permeation/30 seconds relaxation to 12 minutes/45 seconds. As a result of this modification, it was estimated that the system could be operated for 17 months before the membranes would need to be cleaned; (4) 10/30 cycle fouling rates at fluxes of 15 and 18 gfd were approximately 1.1 psi/day and 9.4 psi/day, respectively. These rates are significantly higher than what was observed while operating with the 10/10 cycle; (5) It was estimated that implementation of the 10/30 cycle would result in an approximate 20% reduction of the total power requirements, and thus costs, for the full-scale MBR facility.

Improving Program Efficiency by Packing Instructions into Registers

New processors, both embedded and general purpose, often have conflicting design requirements involving space, power, and performance. Architectural features and compiler optimizations often target one or more design goals at the expense of the others. This paper presents a novel architectural and compiler approach to simultaneously reduce power requirements, decrease code size, and improve performance by integrating an instruction register file (IRF) into the architecture. Frequently occurring instructions are placed in the IRF. Multiple entries in the IRF can be referenced by a single packed instruction in ROM or L1 instruction cache. Unlike conventional code compression, our approach allows the frequent instructions to be referenced in arbitrary combinations. The experimental results show significant improvements in space and power, as well as some improvement in execution time when using only 32 entries. These advantages make packing instructions into registers an effective approach for improving overall efficiency.

Modifying cochlear implant design: advantages of placing a return electrode in the modiolus.

A modiolar return electrode significantly increases the current flow across spiral ganglion cells into the modiolus, and may decrease the cochlear implant's power requirements. Ideal cochlear implants should maximize current flow into the modiolus to stimulate auditory neurons. Previous efforts to facilitate current flow through the modiolus included the fabrication and use of precurved electrodes designed to "hug" the modiolus and silastic positioners designed to place the electrodes closer to the modiolus. In contrast to earlier efforts, this study explores the effects of return electrode placement on current distributions in the modiolus. The effects of return electrode positioning on current flow in the modiolus were studied in a Plexiglas model of the cochlea. Results of model measurements were confirmed by measurements in the modiolus of human temporal bones. The return electrode was placed either within the modiolus, or remotely, outside the temporal bone, simulating contemporary cochlear implant configurations using monopolar stimulation. Cochlear model results clearly show that modiolar current amplitudes can be influenced significantly by the location of the return electrode, being larger when placed into the modiolus. Temporal bone data show similar findings. Voltages recorded in the modiolus are, on average, 2.8 times higher with the return electrode in the modiolus compared with return electrode locations outside the temporal bone. Placing a cochlear implant's return electrode in the modiolus should significantly reduce its power consumption. Reducing power requirements should lead to improved efficiency, safer long-term use, and longer device life.

Speech recognition with a cochlear implant using triphasic charge-balanced pulses

ObjectiveTypically, symmetrical charge-balanced biphasic current pulses are used in cochlear implants to ensure biological safety. Theoretically, monophasic pulses are more effective, but potentially noxious, stimuli. In this study we charge-balanced such monophasic pulses during selected non-stimulated intervals, effectively leading to triphasic pulses with a 4:1 amplitude ratio between the cathodic and anodic phases. Apart from ensuring safety, this is also expected to reduce power consumption and channel interaction. Material and MethodsSeven experienced Clarion CII cochlear implant users with a multichannel (12–16 channels) monopolar continuous interleaved sampling (CIS) strategy participated in the study. Three different CIS strategies were fitted using the Clarion Research Interface (CRI-2). The reference was an implementation of each subject's own CIS program. The two strategies tested used triphasic pulses on the same channels, one with half-wave rectification (TP-HWR) and one without rectification (TP-NoR) at the input. Directly after fitting (i.e. without any training), speech perception (phoneme score on consonant–vowel–consonant words) was measured in silence (sound-only) and in speech-shaped background noise with signal:noise ratios (SNRs) of +5 and 0 dB. ResultsSpeech perception with the reference via the CRI-2 was equal to that of the free-field condition with the subjects’ own speech processor. With the TP-NoR strategy, speech perception improved significantly (from 89% to 93%) in silence and in the 0-dB SNR condition (from 43% to 49%). With a SNR of +5 dB, performance was stable at ≈66%. With the TP-HWR strategy, performance increased significantly in the 0- and +5-dB SNR conditions, to 55% and 74%, respectively. Power consumption was reduced in both strategies, to 30% and 36% for TP-HWR and TP-NoR, respectively. Conclusion The new triphasic strategies are most promising, with respect to both their improved speech perception and reduced power requirements. The optimal parameters will have to be identified following long-term use.

Efficient, high-frequency bulk phase modulator.

An efficient, 10.4-GHz bulk phase modulator is demonstrated that produces frequency-modulated optical bandwidths in excess of 300 GHz in a double-pass configuration with modest microwave drive power. The waveguide resonator design employs velocity matching to maximize phase-modulation efficiency and a modified form of cutoff waveguide coupling to achieve a high microwave cavity Q factor that reduces power requirements. The measured microwave performance of the modulator agrees well with performance predicted from fully anisotropic, three-dimensional numerical simulations.

DNA mutation detection in a polymer microfluidic network using temperature gradient gel electrophoresis.

A miniaturized system for DNA mutation analysis, utilizing temperature gradient gel electrophoresis (TGGE) in a polycarbonate (PC) microfluidic device, is reported. TGGE reveals the presence of sequence heterogeneity in a given heteroduplex sample by introducing a thermal denaturing gradient that results in differences between the average electrophoretic mobilities of DNA sequence variants. Bulk heater assemblies are designed and employed to externally generate temperature gradients in spatial and temporal formats along the separation channels. TGGE analyses of model mutant DNA fragments, each containing a single base substitution, are achieved using both single- and 10-channel parallel measurements in a microfluidic platform. Additionally, a comprehensive polymer microfluidic device containing an integrated microheater and sensor array is developed and demonstrated for performing spatial TGGE for DNA mutation analysis. The device consists of two PC modular substrates mechanically bonded together. One substrate is embossed with microchannels, and the other contains a tapered microheater, lithographically patterned along with an array of temperature sensors. Compared with the external heating approaches, the integrated platform provides significant reduction in power requirement and thermal response time while establishing more accurate and highly effective control of the temperature gradient for achieving improved separation resolution.

An ultrasonic transducer array for velocity measurement in underwater vehicles

A correlation velocity log (CVL) is an ultrasonic navigation aid for marine applications, in which velocity is estimated using an acoustic transmitter and a receiver array. CVLs offer advantages over Doppler velocity logs (DVLs) in many autonomous underwater vehicle (AUV) applications, since they can achieve high accuracy at low velocities even during hover manoeuvres. DVLs require narrow beam widths, whilst ideal CVL transmitters have wide beam widths. This gives CVLs the potential to use lower frequencies thus permitting operation in deeper water, reducing power requirements for the same depth, or allowing the use of smaller transducers. Moving patterns in the wavefronts across a 2D receiver array are detected by calculating correlation coefficients between bottom reflections from consecutive transmitted pulses, across all combinations of receiver pairings. The position of the peak correlation value, on a surface representing receiver-pairing separations, is proportional to the vessel's displacement between pulses. A CVL aimed primarily for AUVs has been developed. Its acoustical and signal processing design has been optimised through sea trials and computer modelling of the sound field. This computer model is also used to predict how the distribution of the correlation coefficients varies with distance from the peak position. Current work seeks to increase the resolution of the peak estimate using surface fitting methods. Numerical simulations suggest that peak estimation methods significantly improve system precision when compared with simply identifying the position of the maximum correlation coefficient in the dataset. The peak position may be estimated by fitting a quadratic model to the measured data using least squares or maximum likelihood estimation. Alternatively, radial basis functions and Gaussian processes successfully predict the peak position despite variation between individual correlation datasets. This paper summarises the CVL's main acoustical features and signal processing techniques and includes results of sea trials using the device.