Margin Improvement Research Articles

First-trial protective step performance before and after short-term perturbation practice in people with Parkinson's disease.

Protective steps are critical for fall prevention and are altered in people with Parkinson's disease (PD). Previous work suggests that perturbation training, in which patients are exposed to repeated slips, may improve protective postural responses. However, these studies typically take the average performance of several postural responses before and after training. To reduce falls in the community, training must improve protective stepping after the first perturbation exposure. To date, no investigations have examined whether first-trial protective stepping is improved after training in people with PD. First-trial protective stepping was measured in 14 people with PD and 9 healthy adults before and 24h after 1day of perturbation training. The primary outcome was margin of stability after a perturbation, a measure of protective stepping effectiveness. Margin of stability for the first perturbation was significantly (p = 0.001) improved on day 2 compared to before perturbation practice (day 1) in both groups. Furthermore, improvement in margin of stability was correlated with age and baseline stepping performance, such that older individuals and people with worse baseline performance showed the most pronounced improvement. Improving the first loss of balance after training is critical if such training is to reduce falls in people with PD. The observed improvement in first-trial protective stepping provides further support for perturbation training as a potential tool to improve protective steps and reduce falls in people with PD.

Design of a high-performance centrifugal compressor with new surge margin improvement technique for high speed turbomachinery

This paper presents the design of a centrifugal compressor for high-speed turbomachinery. The main focus of the research is to develop a centrifugal compressor with improved aerodynamic performance. As a meridional frame has a significant effect on overall performance of the compressor, special attention has been paid to the end wall contours. The shroud profile is design with bezier curve and hub profile with circular arc contour. The blade angle distribution has been arranged in a manner that it merges with single value at impeller exit. The rake angle is positive at leading edge and negative at trailing edge with identical magnitude. Furthermore, three-dimensional straight line element approach has been used for this design for better manufacturability. The verification of the aerodynamic performance has been carried out using CFD software with consideration of a single blade passage and vaneless diffuser. The result has been compared with matching size aftermarket compressor stage gas stand data. The compressor stage with Trim 55 provides 34% increase in choke flow at 210000 RPM as compared to gas stand data with 87% peak stage efficiency at 110000 RPM. In addition, new surge margin improvement technique has been proposed by means of diffuser enhancement. This technique provides an average of 16% improvement in surge margin compared to standard diffuser stage with 55 trim compressor impeller. The mechanical integrity has been validated at maximum RPM with the aluminum alloy 2014-T6 as a fabrication material.

Dynamic performance analysis, stability margin improvement and transfer power capability enhancement in DFIG based wind turbines at weak ac grid conditions

Wind farms are usually located in remote areas far away from utility grid and load centers. Hence, long transmission lines, used between wind farms and utility grid, result in a low value for the grid strength at connection point. This paper first studies stability of the grid connected DFIG wind turbine taking the PLL dynamics into account, and then presents an efficient control approach to stabilize the system and to enhance transfer power capability at weak grid conditions. Hence, unified dynamic modeling of the whole DFIG, including dynamics of the PLL, stator flux, rotor current, drive train, dc-link, rotor side converter (RSC) and grid side converter (GSC) current controllers, dc-link voltage and generator speed controllers, and grid is presented. Then, small signal stability of the full system is carried out and impact of the grid short circuit ratio (SCR) on stability of the system is examined. Next, rotor control structure is modified to increase the stability margin and transfer power capability under weak grid conditions. By the modified control structure, the grid SCR is virtually increased to enhance the system performance at weak grid connections. Finally, results of theoretical analyses are verified by time domain simulations conducted in MATLAB-Simulink environment.

The impact of casing groove location on the flow instability in a counter-rotating axial flow compressor

To make up the lack of the experimental and numerical investigations about the grooved casing treatment (CT) applied in counter-rotating axial flow compressors (CRAC), the effects of circumferential single grooved CT on the stability enhancement were investigated in the rear rotor of a low-speed CRAC with numerical simulations. The main purpose was to gain a better understanding of the application principle of casing groove and the associated control mechanisms in the CRAC. Parametric studies show that the optimal position of the groove should be located near the blade leading edge in terms of stall margin improvement (SMI) and efficiency enhancement at the near stall condition. Due to the impact of casing groove on tip leakage flow (TLF), the blade tip unloading effect, redirection effect and the compound effect of suction–injection are all beneficial to the SMI. Detailed observation of flow structures illustrates that it is more effective to improve flow stability by controlling the critical TLF released from about mid-chord and the stall inception process may be probably changed due to the direct effect of groove on the main TLF released near the blade leading edge. Additionally, the effects that the groove has on rotor outflow blockage, backward axial momentum flux and TLF momentum perpendicular to the blade tip camber inside the tip gap are also studied in the paper.

Voltage stability margin improvement using hybrid non‐linear programming and modified binary particle swarm optimisation algorithm considering optimal transmission line switching

A new method is proposed for economic improvement of voltage stability margin. The preventive control facilities include demand response, active/reactive generation rescheduling and load shedding. Transmission line switching is also considered as a new solution for economic improvement of voltage stability margin. The best candidate transmission lines for switching action are selected using modified binary particle swarm optimisation algorithm and the voltage stability subproblem is formulated as non-linear programming model. In order to verify effectiveness of the proposed method, comprehensive simulations are performed on the IEEE 118-bus test system. The results indicate high efficiency of the proposed method in identifying the best lines and also decreasing the cost of voltage stability margin improvement. As a result, for the same voltage stability margin, the cost is decreased using optimal transmission line switching.

Evaluation of static noise margin of 6T SRAM cell using SiGe/SiC asymmetric dual‐kspacer FinFETs

This work aims to investigate the device performance of silicon–germanium (SiGe)/Si carbide (SiC) source/drain (S/D) asymmetric dual-k spacer underlap Fin-field-effect transistor (SiGe/SiC-AsymD-k FinFET) with Si channel for high performance and robust SRAM cell. Strain-induced mobility enhancement due to the Si1−x Ge x /Si1−y C y S/D leads to a significant drive current enhancement of the proposed device. The introduced asymmetric dual-k spacer at source side offers excellent gate control over the channel. By exploiting asymmetry in current, the authors prove that it is possible to achieve mitigation of read–write conflict in 6T SRAM bit cell. SiGe/SiC-AsymD-k FinFET SRAM offers 8.39% improvement in hold static noise margin, 14.28% in read and 18.06% in write mode over conventional FinFET-based 6T SRAM bit cell. When compared to conventional FinFET 6T SRAM bit cell, the proposed 6T SRAM bit cell shows lesser temperature sensitivity of cell stability.

Numerical analysis of the circumferential grooves casing treatment in a counter-rotating axial flow compressor

The impact of the circumferential grooves casing treatment over the rear rotor (R2) in a counter-rotating axial flow compressor has been investigated based on numerical simulations. The main purpose is to understand the effects of grooved casing treatment on the unsteady flow behaviors and the corresponding mechanisms of the stability enhancement in the compressor. The results show that the interface between incoming main flow and tip leakage flow in R2 is pushed downstream obviously and the flow stability is enhanced with grooved casing treatment. The compressor performance at near stall condition is also improved remarkably. The blade loading below the grooves, the incidence angle near the blade tip and the backward axial momentum flux injected into main flow passage through the tip gap are all reduced, which is beneficial to the stall margin improvement. Frequency analysis near the blade tip of R2 indicates that the oscillations with lower frequency are suppressed by the casing grooves and the fluctuating intensity decreases, which also contributes for the enhancement of flow stability. Detailed observation of tip leakage flow structures illustrates that it is more effective to improve the flow stability by controlling the tip leakage flow released from near mid-chord.

A new approach of casing treatment design for high speed compressors running at partial speeds with low speed large scale test

The instability problems tend to be more severe when high speed compressors operate at partial speeds. This paper proposes an economic approach for casing treatment design that suitable to this situation. Aiming at reducing the expensive and time-consuming high-speed casing treatment experiments, the idea of low-speed similitude of high-speed compressors, which was originally practiced in mid-1980 with the purpose of loss reduction, is now extended to simulate the stability enhancement with casing treatment in this paper. The core idea of this approach is to replace a large portion of design processes for the high-speed compressors (the Prototype) with their equivalent large scale model compressors (the Model). Two different transonic rotors with skewed slots and circumferential grooves casing treatments are conducted as examples to demonstrate this approach. Following the selected similarity rules, the Model is firstly acquired by modeling the near stall point of the Prototype. A variety of casing treatments are designed and assessed on the Model. Then a few more promising configurations can thus be selected via low speed experiments. They are believed to have similar tendency on stall margin improvement on the Prototype. Finally, the selected configurations are converted back to the Prototype with based on the rule of similarity and validated by experimental data. In this paper, principles that guarantee the similitude of the flow field at near stall condition and the effectiveness of the casing treatment are discussed.

A Compact-Area Low-VDDmin 6T SRAM With Improvement in Cell Stability, Read Speed, and Write Margin Using a Dual-Split-Control-Assist Scheme

Previous 6T SRAMs commonly employ a wordline voltage underdrive (WLUD) scheme to suppress half-select (HS) disturbs in read and write cycles, at the expense of reduced cell read current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CELL</sub> ) and degraded write margin (WM). This paper proposes the dual-split-control (DSC) scheme, including split WLs and split cell VSS (CVSS), for 6T SRAM to maintain a compact cell area and improve HS cell stability during the read and write cycles without degrading I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CELL</sub> and WM. A segmented CVSS-strapping scheme is developed to suppress the ground bounce on the split-CVSS lines. The CVSS voltage for S6T can be generated by either a constant voltage source or a charge-sharing-based CVSS generation scheme. A 28-nm 256-kb DSC6T SRAM macro was fabricated and achieves a 280-mV lower VDDmin than a conventional 6T SRAM.

Improvement of SRAM stability using read and write assist techniques

The objective of this paper is to demonstrate how to improve the read stability of the SRAM cell using the read assist technique. SRAM cell stability is the primary concern for the present and future technologies due to process variations like Vt and Vdd scaling, etc. So it requires additional circuit techniques such as write and read to assist to improve the stability of SRAM memories. To accomplish the non-destructive read operation, we need to either weaken the pass transistor or strengthen the pull-up transistor during the read operation. Towards decrease of pass transistor strength, we implemented the lower word line voltage as read assist circuit. The lower word line voltage will help the selected and un-selected columns (for higher column mux options) during a read operation. But during write operation the lowered word line voltage scheme will impact the write operation. So, in order to improve the read margin we used read assist technique at the same time to ensure that write operation is successful we combined the negative bit line write assist scheme along with read assist technique. The proposed assist circuit gain the power and read margin improvement of 10%, 30% respectively. We observed the read margin analysis at process, voltage and temperature corners.

Numerical Investigation for the Impact of Single Groove on the Stall Margin Improvement and the Unsteadiness of Tip Leakage Flow in a Counter-Rotating Axial Flow Compressor

A low-speed counter-rotating axial flow compressor (CRAC) with single circumferential grooved casing treatment (CT) was investigated numerically. Both steady and time-accurate numerical calculations were performed to study the effects of the single grooved CTs over the rear rotor on the stability enhancement and the unsteadiness of tip leakage flow (TLF) in the CRAC. Parametric studies indicate that the best position of the single groove should be located near about 20% axial tip chord in terms of the stall margin improvement (SMI). The coincidence of the effective CT locations and the high fluctuating region on blade pressure surface in the smooth wall case shows that the unsteadiness of TLF plays an important role in the stall inception process. Frequency analysis for the static pressure signals near the blade tip shows that both the disappearance of the low frequency components and the suppression of unsteady TLF are beneficial to the SMI. Detailed observation of the flow structures illustrates that the action of the grooves on the different parts of TLF is responsible for the difference of SMI in the CTs. It is more effective to improve the flow stability by controlling the critical TLF released from near the mid-chord.

Investigation on axial effect of slot casing treatment in a transonic compressor

This paper reports the effect of the axial position of the slot casing treatment on the performance of transonic compressor NASA Rotor 67 by unsteady numerical simulation. The interaction of the recirculation in the slots and flow near the blade tip is analyzed to understand the flow mechanisms. The relative importance of the mechanisms of stall margin improvement due to the slot casing treatment is evaluated with the relative weight method. The results show that the bleeding and injecting effect caused by the recirculation is the most important factor that affects the blockage in the blade tip region, which determines the stall margin improvement. When the slots cover the initial position of the tip leakage vortex (TLV) and the boundary layer separation zone downstream the shock, the recirculation is stronger due to the larger pressure difference between the front and rear part of the slots. Consequently, the slot casing treatment can reduce the blockage near the casing more effectively, which results in a larger stall margin improvement. Shifting the slots upstream or downstream will reduce the driving force for the recirculation and the effect extent on the low energy fluid of the slots, which decreases the stall margin improvement.

Co-learning cycles to support the design of innovative farm systems in southern Mali

Farm systems were re-designed together with farmers during three years (2013–2015) in Southern Mali with the aim to improve income without compromising food self-sufficiency. A cyclical learning model with three steps was used: Step 1 was the co-design of a set of crop/livestock technical options, Step 2 the on-farm testing and appraisal of these options and Step 3 a participatory ex-ante analysis of re-designed farm systems incorporating the tested options. Two iterations of the cycle were performed, in order to incorporate farmers’ point of view and researchers’ learning. We worked together with 132 farmers representing four farm types: High Resource Endowed with Large Herd (HRE-LH); High Resource Endowed (HRE); Medium Resource Endowed (MRE) and Low Resource Endowed (LRE) farms. In the first cycle of 2012–2014 farmers re-designed their farms and the reconfigurations were assessed ex ante using the average yields and gross margins obtained in the 2013 on-farm trials. HRE-LH farmers experienced a disappointing decrease in food self-sufficiency and MRE farmers were disappointed by the marginal improvement in gross margin. In a second cycle in 2014–2015, farmer insights gathered during field days and statistical analysis of trial results allowed a better understanding of the variability of option performance and the link with farm context: niches were identified within the farms (soil type/previous crop combinations) where options performed better. The farm systems were re-designed using this niche-specific information on yield and gross margin, which solved the concerns voiced by farmers during the first cycle. Without compromising food self-sufficiency, maize/cowpea intercropping in the right niche combined with stall feeding increased HRE-LH and HRE farm gross margin by 20–26% respectively (i.e. 690 and 545 US$ year−1) with respect to the current farm system. Replacement of sorghum by soyabean (or cowpea) increased MRE and LRE farm gross margin by 29 and 9% respectively (i.e. 545 and 32 US$ year−1). Farmers highlighted the saliency of the niches and the re-designed farm system, and indicated that the extra income could be re-invested in the farm. Our study demonstrates the feasibility and the usefulness of a cyclical and adaptive combination of participatory approaches, on-farm trials and ex-ante analysis to foster learning by farmers and researchers, allowing an agile reorientation of project actions and the generation of innovative farm systems that improve farm income without compromising food self-sufficiency. The re-designed farm systems based on simple, reproducible guidelines such as farm type, previous crop and soil type can be scaled-out by extension workers and guide priority setting in (agricultural) policies and institutional development.

Stability enhancement of an interconnected AC/DC power system through VSC-MTDC operating point adjustment

This paper investigates the improvement of dynamic and transient stability in interconnected AC/DC power systems through operating point adjustment in an embedded VSC-MTDC network. Hopf Bifurcation (HB) is known to result in oscillatory instability in the power system, therefore a sufficient margin to HB has to be maintained to enhance the dynamic stability and ensure a secure operation of the system. The enhancement of dynamic stability is based on the adjustment of the MTDC converters’ controller setpoints to drive the system away from HB point and increase the damping of oscillatory modes. The variation of each setpoint is calculated in proportion to the eigenvalue sensitivity to the respective setpoint. On the other hand, transient stability enhancement is based on operating point adjustment according to Power Transfer Distribution Factors (PTDFs) with the aim to reduce inter-area power flow over AC lines. The proposed method is applied to a VSC-MTDC network interconnecting two IEEE 14-bus sections. The results show an improvement in the system's stability margin in case of various disturbances such as load increase and short circuit fault. Time-domain simulations in DIgSILENT are used to corroborate the results obtained through small signal stability analysis.

Exploring the economic potential of reducing broiler lameness

ABSTRACT1. The present study was designed first to explore the potential economic benefits of adopting management practices to reduce lameness in broiler farms, and second to explore farmers’ possible perceptions of this potential in the Swedish context. The likely financial effects were addressed using a normative economic model, whereas a questionnaire-based survey was used to obtain in-depth knowledge about the perceptions of a group of broiler farmers in Sweden.2. The three alternative practices (out of 6 tested) which realised the greatest improvements in gross margin and net return to management compared to the conventional practice were feeding whole wheat, sequential feeding and meal feeding.3. The model showed that the negative effect of feeding whole wheat on feed conversion rate was outweighed by the effect of a low feed price and the associated decrease in feed costs. The price of wheat played a major role in the improvement of economic performance, whereas the reduction of lameness itself made a relatively minor contribution.4. Apparently, the surveyed farmers do not recognise the potential of the positive effects of changing feed or feeding practices on both broiler welfare and farm economics although their implementation can be of great importance in the broiler sector where profit margins are very tight.​

Quasi-Schottky-Barrier UTBB SOI MOSFET for Low-Power Robust SRAMs

This paper presents a low-power robust static random access memory (SRAM) using a novel quasi-Schottky-barrier ultrathin body and ultrathin buried oxide (UTBB) silicon-on-insulator (SOI) device. In the proposed device, the drain terminal is highly doped and a metallic source terminal is used. Given the proposed structure, asymmetric characteristics will be achieved according to the drain–source bias voltage ( ${V}_{\text {DS}})$ . These characteristics of the proposed device are extensively analyzed and compared with a conventional symmetric UTBB SOI device. The asymmetry nature of the proposed device will lead to the mitigated read–write conflict of the 6T-SRAM cell. The simulation results show a leakage reduction of 18% at ${V}_{\text {DD}} = 1$ V in comparison with the 6T-SRAM cell realized by conventional symmetric UTBB SOI device. Furthermore, in comparison with the conventional 6T-SRAM, the realized cell shows a 54% improvement in read static noise margin, 6.6% higher write margin, and $3.1\times $ faster write at the cost of a longer access time. To achieve a practical read access time, we utilize split bitline approach.

Investigation of 6T SRAM memory circuit using high-k dielectrics based nano scale junctionless transistor

In this paper the Dual Metal Surround Gate Junctionless Transistor (DMSGJLT) has been implemented with various high-k dielectric. The leakage current in the device is analysed in detail by obtaining the band structure for different high-k dielectric material. It is noticed that with increasing dielectric constant the device provides more resistance for the direct tunnelling of electron in off state. The gate oxide capacitance also shows 0.1 μF improvement with Hafnium Oxide (HfO2) than Silicon Oxide (SiO2). This paved the way for a better memory application when high-k dielectric is used. The Six Transistor (6T) Static Random Access Memory (SRAM) circuit implemented shows 41.4% improvement in read noise margin for HfO2 than SiO2. It also shows 37.49% improvement in write noise margin and 30.16% improvement in hold noise margin for HfO2 than SiO2.

마이크로그리드를 기반으로 한 중소 산업용수용가의 최대수요전력 저감방안

Recently, the power consumption of industrial consumer has increased rapidly, causing problems such as lack of power reserve margin in summer and winter, and therefore there is a growing need for maximum demand power management to consumers. In this paper, we studied small microgrid system consisting of battery ESS and photovoltaic power system, applied to small and medium sized factories to reduce the maximum demand power of daily industrial power load. To verify the validity of the study, we simulated a small microgrid system using Matlab/Simulink software. As a result of applying the simulation to small and medium sized plants that consume a lot of power, it is confirmed that there is a 13% reduction in demand compared to the existing maximum demand power. This result is expected to contribute to the improvement of the power reserve margin.

Flow Mechanism for Stall Margin Improvement via Axial Slot Casing Treatment on a Transonic Axial Compressor

Flow Mechanism for Stall Margin Improvement via Axial Slot Casing Treatment on a Transonic Axial Compressor

Effect of splitter leading edge location on performance of an automotive turbocharger compressor

Design of centrifugal compressors can be accomplished using methods provided in text books and open literature. In this general approach, after determination of dimensions in meridional plane, blade profiles are designed using aerodynamic methods. Then, some blades are trimmed at the beginning to avoid inlet blockage. But there is no clear guidance on how this trimming must be performed. With this widely implemented method, splitter blades have the same profile as main ones.In this research, blade profiles and dimensions of the compressor impeller are not changed while the effect of changes in the position and angle of splitters leading edge are investigated. An optimization scheme is performed to find the best configuration over the complete operating curve of the compressor using genetic algorithm and considering structural aspect of the problem. CFD codes with experimental support are used to predict the compressor performance and flow field specifications with the original impeller as well as the modified one. After taking into account some geometrical details, a new impeller is manufactured based on the modified design and tested in a wide range of operating conditions. Results show 2.7 points improvement in efficiency at the nominal point and 5% decrease in impeller moment inertia. No change in choke behavior, but notable improvement in surge margin of the modified compressor is observed. This is an important achievement in all applications of centrifugal compressors, especially in turbochargers.