239 research outputs found
Low-PAPR layered/enhanced ACO-SCFDM for optical-wireless communications
No full textIn this letter, we propose layered/enhanced asymmetrically clipped optical single-carrier frequency-division multiplexing (L/E-ACO-SCFDM) for optical-wireless communications. L/E-ACO-SCFDMhas a lower computational complexity and peak-to-average power ratio (PAPR) than L/E-ACO orthogonal frequency-division multiplexing (L/E-ACO-OFDM). The computational complexity of the simplified transmitter in L/EACO-SCFDM with R layers is (2 - 2/2R)O(N), which is lower than the computational complexity of (2 - 2/2R)O(Nlog2N) in L/E-ACO-OFDM. At a complementary cumulative distribution function of 10-3, the PAPR of L/E-ACO-SCFDM is approximately 4.2, 3.4, and 2.7 dB lower than that of L/E-ACO-OFDM for 2, 3, and 4 layers, respectively. The simulation results indicate that L/E-ACO-SCFDM has better performance than L/E-ACOOFDM under the transmitter nonlinearity and multipath fading.</p
Faster-than-Nyquist non-orthogonal frequency-division multiplexing for visible light communications
No full textIn this paper, we propose a faster-than-Nyquist (FTN) non-orthogonal frequency-division multiplexing (NOFDM) scheme for visible light communications (VLC) where the multiplexing/demultiplexing employs the inverse fractional cosine transform (IFrCT)/FrCT. Different to the common fractional Fourier transform-based NOFDM (FrFT-NOFDM) signal, FrCTbased NOFDM (FrCT-NOFDM) signal is real-valued, which can be directly applied to the VLC systems without the expensive up-conversion and thus it is more suitable for the cost-sensitive VLC systems. Under the same transmission rate, FrCT-NOFDM signal occupies smaller bandwidth compared to OFDM signal. When the bandwidth compression factor &#x03B1; is set to 0.8, 20&#x0025; bandwidth saving can be obtained. Therefore, FrCT-NOFDM has higher spectral efficiency and suffers less high-frequency distortion compared to OFDM, which benefits the bandwidthlimited VLC systems. As the simulation results show, bit error rate performance of FrCT-NOFDM with &#x03B1; of 0.9 or 0.8 is better than that of OFDM. Meanwhile, FrCT-NOFDM has a superior security performance. In conclusion, FrCT-NOFDM shows the potential for application in the future VLC systems.</p
Optically-generated ultrasound for non-invasive brain stimulation
No full textNeuromodulation plays a crucial role in facilitating research into brain function and enabling treatments for neurological and psychiatric disorders. In brain research, current non-invasive tools face challenges when studying brain sub-regions due to their limited spatial resolution, which can barely reach a scale of 100 μm. Moreover, precise control over the volume of tissue activated (VTA) is needed to effectively target diverse-shaped brain regions, such as ocular dominance columns. Similarly, in disease treatment, the lack of sufficient spatial resolution poses obstacles in restoring normal vision using existing FDA-approved retina prostheses for retinitis pigmentosa.
To address these challenges, my thesis work focuses on the development of optically-generated ultrasound devices for non-invasive brain stimulation and implantable retina prostheses. Firstly, to meet the need for non-invasive neuromodulation with ultrahigh precision, we have developed an optically-generated focused ultrasound device. By embedding candle soot nanoparticles in a curved polydimethylsiloxane pad, this device generates a transcranial ultrasound focus at 15 MHz with an ultrahigh lateral resolution of 83 μm. This resolution is two orders of magnitude smaller than conventional transcranial-focused ultrasound, enabling successful submillimeter transcranial stimulation in vivo targeting the mouse motor cortex.
Addressing the requirement for a customized VTA in specific brain sub-regions, we have developed an optically-generated Bessel beam ultrasound device. This device was specifically designed to target brain columns with an elongated acoustic focus, and it successfully achieved a VTA with a lateral resolution of 152 μm and an axial resolution of 1.93 mm. The stimulation capability of the device has been confirmed through immunofluorescence imaging, which showed that the stimulation depth in mouse brains reached up to 2.2 mm.
Furthermore, in order to address the need for an ultrahigh spatial resolution in retina prosthesis, we have developed an optically-generated ultrasound film as a subretinal prosthesis. In proof-of-concept experiments using blind rat retina, this film
has successfully achieved retina stimulation ex vivo.
In conclusion, optically-generated ultrasound devices offer promising opportunities for brain science research and disease treatments. They revolutionize non-invasive brain stimulation with ultrahigh precision and customized VTA for studying brain sub-regions. Additionally, they hold the potential for enhancing spatial resolution in retina prostheses, bringing hope to individuals with retinal disorders.2024-09-08T00:00:00
Consumers’ Attitudes towards Surcharges on Distributed Renewable Energy Generation and Energy Efficiency Programs
No full textabstract: Increasing penetration of energy efficiency programs and distributed renewable energy generation has imposed significant challenges for utilities to recoup their large upfront costs. There is a heated debate on what surcharges should be implemented to help the utilities recover their fixed costs; however, very few studies focus on consumers’ attitudes regarding this topic. This study surveys about 190 residential consumers throughout the United States in November 2015, investigating their preferences and attitudes towards extra demand charges and volumetric energy price increases. We apply probit models and regress consumers’ attitudes on selected socio-demographic and behavioral variables. The results indicate the homeowners are more likely to prefer demand charges when compared to renters. The demographic and behavioral factors impact consumers’ perception of bill savings from energy efficiency programs or solar panel installation and also influence how consumers perceive the fairness of utilities recovering revenue losses by increasing volumetric energy price. In this paper, we demonstrate there is preference heterogeneity among consumers and that policy makers should be aware of such preference heterogeneity and apply policy targeting based on the identified demographics and behavioral factors impacting consumer preferences.The final version of this article, as published in Sustainability, can be viewed online at: http://www.mdpi.com/2071-1050/9/8/147
Peer Effects and Voluntary Green Building Certification
No full textabstract: Empirical evidence is provided to show that peer effects have statistically significant and positive impacts on the diffusion of green building certificates. Application and approval records of green certificates by commercial buildings in NY and AZ are used. The challenge of self-selection is addressed by the usage of fixed effects and the challenge of reflection is addressed by the time lag delay between a building’s application and its approval. Empirical results show that an additional approved LEED certificate within a zip code will increase the probability of a commercial building in the same zip code to apply for a LEED certificate by 3–4 percentage points; an additional approved Energy Star certificate within a zip code will increase the probability of a commercial building in the same zip code to apply for an Energy Star certificate by 1–2 percentage points
Boundary Element Analysis of the Stress Distribution Around Multiple Fractures: Implications for the Spacing of Perforation Clusters of Hydraulically Fractured Horizontal Wells
No full textMonte Carlo-Based VaR Estimation and Backtesting Under Basel III
No full textValue-at-Risk (VaR) is a key metric widely applied in market risk assessment and regulatory compliance under the Basel III framework. This study compares two Monte Carlo-based VaR models using publicly available equity data: a return-based model calibrated to historical portfolio volatility, and a CAPM-style factor-based model that simulates risk via systematic factor exposures. The two models are applied to a technology-sector portfolio and evaluated under historical and rolling backtesting frameworks. Under the Basel III backtesting framework, both initially fall into the red zone, with 13 VaR violations. With rolling-window estimation, the return-based model shows modest improvement but remains in the red zone (11 exceptions), while the factor-based model reduces exceptions to eight, placing it into the yellow zone. These results demonstrate the advantages of incorporating factor structures for more stable exception behavior and improved regulatory performance. The proposed framework, fully transparent and reproducible, offers practical relevance for internal validation, educational use, and model benchmarking
Pressure Transient Characteristics of Hydraulically Fractured Horizontal Shale Gas Wells
No full textAbstract
Shale gas wells require a long horizontal lateral intersecting multiple hydraulic fractures to be economically viable. Because of the nature of ultralow permeability of shale matrix, it would take a significant long period of time for a well producing in transient flow regimes. Therefore, pressure transient characteristics for such a gas well is of considerable importance in both evaluation of fracturing treatment by estimating fracture and reservoir parameters and prediction of the long-term production behavior of wells in gas recovery.
The pressure transient response for a horizontal shale gas well with multiple transverse fractures is controlled by a specific combination of reservoir properties and well configuration. Focused on Marcellus shales, this paper investigates the characteristics of pressure transient response under a number of factors and flow mechanisms. The factors that are considered include matrix permeability, conductivity of hydraulic fractures, cluster spacing, and size/enhanced permeability of stimulated zone. The impacts of gas desorption and stress-dependent fracture conductivity on pressure transient behavior are also illustrated. This study provides insights into the pressure transient characteristics during shale gas well production.</jats:p
Pressure transient testing and productivity analysis for horizontal wells
No full textThis work studied the productivity evaluation and well test analysis of horizontal wells. The major components of this work consist of a 3D coupled reservoir/wellbore model, a productivity evaluation, a deconvolution technique, and a nonlinear regression technique improving horizontal well test interpretation.
A 3D coupled reservoir/wellbore model was developed using the boundary element method for realistic description of the performance behavior of horizontal wells. The model is able to flexibly handle multiple types of inner and outer boundary conditions, and can accurately simulate transient tests and long-term production of horizontal wells. Thus, it can serve as a powerful tool in productivity evaluation and analysis of well tests for horizontal wells.
Uncertainty of productivity prediction was preliminarily explored. It was demonstrated that the productivity estimates can be distributed in a broad range because of the uncertainties of reservoir/well parameters.
A new deconvolution method based on a fast-Fourier-transform algorithm is presented. This new technique can denoise "noisy" pressure and rate data, and can deconvolve pressure drawdown and buildup test data distorted by wellbore storage. For cases with no rate measurements, a "blind" deconvolution method was developed to restore the pressure response free of wellbore storage distortion, and to detect the afterflow/unloading rate function using Fourier analysis of the observed pressure data. This new deconvolution method can unveil the early time behavior of a reservoir system masked by variable-wellbore-storage distortion, and thus provides a powerful tool to improve pressure transient test interpretation. The applicability of the method is demonstrated with a variety of synthetic and actual field cases for both oil and gas wells.
A practical nonlinear regression technique for analysis of horizontal well testing is presented. This technique can provide accurate and reliable estimation of well-reservoir parameters if the downhole flow rate data are available. In the situation without flow rate measurement, reasonably reliable parameter estimation can be achieved by using the detected flow rate from blind deconvolution. It has the advantages of eliminating the need for estimation of the wellbore storage coefficient and providing reasonable estimates of effective wellbore length. This technique provides a practical tool for enhancement of horizontal well test interpretation, and its practical significance is illustrated by synthetic and actual field cases
Parameter Identification, Simulation, Linearization and Validation of a Ship Propulsion System
No full textThis Thesis is written to obtain the Master of Science degree of Maritime Technology at Delft University of Technology. It describes a research regarding with the calibration(parameter identification), validation and linearization of a ship propulsion system model. In the meantime, the Thesis is also one sub-project under the research program "Potential of Hardware-In-the-Loop Simulation in the Towing Tank" held by Dr.Ir.A.Vrijdag. HIL (Hardware-In-the-Loop) Simulation is widely used in Engineering Technology Field, and has been proved to be a very effective, highly-efficient, economical and environmental friendly strategy in the test and development of engineering control systems. The model scale ship tests nowadays, on the other hand, need to be improved and HIL Simulation provides an innovative & creative way, therefore it is reasonable to start the program and explore more in this field
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