Penetration Limit Research Articles

Distributed generation planning in active distribution network considering demand side management and network reconfiguration

This paper proposes a novel distributed generation (DG) planning methodology in active distribution network considering both demand side management and network reconfiguration. The objective function of the planning model is to minimize the total cost over the planning horizon, including investment cost of DG, operation and management cost of DG, fuel cost of DG, active management cost of DG, and demand side management cost. The constraints contain not only traditional DG investment and electrical restrictions (for instance, limitation of DG penetration, constraint of nodal voltage, constraint of branch capacity, etc.), but also the various restrictions of active management measures including regulating the on-load tap changer of transformer, controlling the output power of DG, demand side management and network reconfiguration. It is a large-scale mixed integer nonlinear programming model, which cannot be effectively solved by a single algorithm. Based on the idea of decomposition and coordination, the planning model is converted to a three-layer programming model. A hybrid solving strategy is developed to solve the model, in which differential evolution algorithm is used to determine the type, location and capacity of DG, and tree structure encoding-partheno genetic algorithm and primal–dual interior point method are applied to simulate the operation of active distribution network and find out the optimal operation state for each scenario. Case studies are carried out on a 61-bus active distribution network in East China, and results show that the total cost over the planning horizon can be reduced about 3.8% when demand side management and network reconfiguration are considered.

Clearing for Deep Tissue Imaging.

Biologic tissues are generally opaque due to optical properties that result in scattering and absorption of light. Preparation of tissues for optical microscopy often involves sectioning to a thickness of 50-100 µm, the practical limits of light penetration and recovery. A researcher who wishes to image a whole tissue must acquire potentially hundreds of individual sections before rendering them into a three-dimensional volume. Clearing removes strongly light-scattering and light-absorbing components of a tissue and equalizes the refractive index of the imaging medium to that of the tissue. After clearing, the maximum depth of imaging is often defined by the microscope optics rather than the tissue. Such visibility enables the interrogation of whole tissues and even animals without the need to section. Researchers can study a biological process in the context of its three-dimensional environment, identify rare events in large volumes of tissues, and trace cells and cell-cell interactions over large distances. This article describes four popular clearing protocols that are relevant to a wide variety of scenarios across biologic disciplines: CUBIC, CLARITY, 3DISCO, and SeeDB. © 2018 by John Wiley & Sons, Inc.

Synergistic interfacial reinforcement of carbon fiber/polyamide 6 composites using carbon-nanotube-modified silane coating on ZnO-nanorod-grown carbon fiber

We report an experimental study on improvement of mechanical properties of a multiscale hybrid composite consisting of in-situ polymerized polyamide-6 and zinc oxide nanorod(ZnO NR)-grown woven carbon fiber (WCF) coated with carbon nanotube(CNT)-modified silane. The ZnO growth process and silane coating process were performed on the fiber surface, and then the composite was fabricated by ultra-fast (<30 s from infusion to polymerization) thermoplastic resin transfer molding technique with extremely low viscosity of resin. The ZnO NRs formed mechanical interlocking with polymer matrix, and at the same time, the CNTs-modified silane layer on WCFs and ZnO NRs formed covalent bond with the matrix; therefore, they induced strong interaction between matrix and fibers, thereby resulting in remarkable improvements in the mechanical properties of the composite. The morphology, coating thickness and composition of the CNTs-modified silane/ZnO/WCF surface according to amount of the silane coupling agent were analyzed and their effects on mechanical properties of the composite were investigated. As compared to neat composites, multiscale hybrid composites showed up to 32 and 41% increases in tensile modulus and strength, respectively, and 107, 179 and 159% increases in in-plane shear strength, absorbed impact energy and penetration limit, respectively.

Improved stochastic fractal search algorithm with chaos for optimal determination of location, size, and quantity of distributed generators in distribution systems

In the power system operation, the reduction of the power loss in distribution systems has significance in the reduction of operating cost. In this paper, a novel chaotic stochastic fractal search (CSFS) method is implemented for determining the optimal siting, sizing, and number of distributed generation (DG) units in distribution systems. The objective of the optimal DG placement problem is to minimize the power loss in distribution systems subject to the constraints such as power balance, bus voltage limits, DG capacity limits, current limits, and DG penetration limit. The proposed CSFS method improves the performance of the original SFS by integrating chaotic maps into it. On the other hand, ten chaotic maps are utilized to replace the random scheme of the original SFS to enhance its performance in terms of accuracy of solution and convergence speed, corresponding to ten chaotic variants of the SFS where variant being chosen is the best chaotic variant regarding search performance. For solving the problem, the CSFS is implemented to simultaneously find the optimal siting and sizing of DG units and the optimal number of DG units will be obtained via comparing optimal results from different numbers of DG in the problem. The proposed method is tested on the IEEE 33-bus, 69-bus, and 118-bus radial distribution systems. The obtained results from the CSFS are verified by comparing to those from the original SFS and other methods in the literature. The result comparisons indicate that the proposed CSFS method can obtain higher quality solutions than the original SFS version and many other methods in the literature for the considered cases of the test systems. Moreover, the incorporation of chaos theory allows performing the search process at higher speeds. Therefore, the proposed CSFS method can be a very promising method for solving the problem of optimal placement of DG units in distribution systems.

A Framework for Assessing Renewable Integration Limits With Respect to Frequency Performance

The increasing penetration of nonsynchronous renewable energy sources (NS-RES) and demand side-technologies alter the dynamic characteristics, and particularly, the frequency behavior of a power system. Given this, we propose a framework for assessing renewable integration limits concerning power system frequency performance using a time-series scenario based approach. By considering a large number of future scenarios and their sensitivities with respect to different parameters, we can identify maximum nonsynchronous instantaneous penetration limits for a wide range of possible scenarios. Further, we derive a dynamic inertia constraint and incorporate it into the market dispatch model to reduce the detrimental impacts of high NS-RES penetration on the frequency performance. The results using the Australian future grid as a test case show that such an explicit inertia constraint ensures power system frequency stability for all credible contingencies. To improve the frequency performance, we assess and quantify the contribution of a wide range of technologies, including synchronous condensers, synthetic inertia from wind farms and a governor-like response from de-loaded wind farms. The results show that the last option is the most effective one.

A novel stochastic fractal search algorithm for optimal allocation of distributed generators in radial distribution systems

This paper presents an application of a novel stochastic fractal search algorithm (SFSA) for solving the optimal allocation of distributed generators (OADG) problem in radial distribution systems (RDSs). The SFSA method is a newly efficient meta-heuristic algorithm inspired by the growing process of nature by using a mathematical idea known as fractal for solving optimization problems. The advantages of the SFSA method are simple implementation and few control parameters. The method is proposed to deal with the OADG problem by minimizing the active power loss, improving the voltage profile, and increasing the voltage stability while satisfying various constraints including active and reactive power balance, bus voltage limits, DG capacity limits, branch current limits, and DG penetration limit. The effectiveness of the proposed SFSA method has been verified on the IEEE 33-bus, 69-bus, and 118-bus RDSs and the obtained results have been validated via comparing to those from other methods in the literature. The result comparisons from the test systems have indicated that the proposed method can obtain higher quality solutions than many other methods for the considered scenarios from the test systems. Therefore, the proposed SFSA can be a very effective and favorable method for solving the OADG problem.

Relevance of antifungal penetration in biofilm-associated resistance of Candida albicans and non-albicans Candida species

The role of penetration limitation in Candida biofilm-associated antifungal resistance remains unclear. Most of the previous work has been done on Candida albicans, although non-albicans (NAC) species are also implicated in invasive candidiasis and the biofilm matrix has been shown to vary amongst different species. Only a few studies have evaluated clinical isolates. This study aimed to determine the relevance of penetration limitation in the antifungal resistance of biofilms formed by C. albicans and NAC clinical isolates, using an agar disk diffusion assay. The penetration of posaconazole and amphotericin B through the biofilms was significantly reduced. Fluconazole, voriconazole and caspofungin showed a superior penetration capacity in C. albicans, Candida tropicalis and Candida parapsilosis biofilms, but exhibited inter-species and strain/isolate variation. Candida krusei biofilms were the most resilient to antifungal permeation. All of the antifungal drugs failed to kill the biofilm cells, independent of penetration, suggesting that the other factors contribute markedly to the recalcitrance of the biofilms.

Optogenetic surface stimulation of the rat cervical spinal cord

Electrical intraspinal microstimulation (ISMS) at various sites along the cervical spinal cord permits forelimb muscle activation, elicits complex limb movements and may enhance functional recovery after spinal cord injury. Here, we explore optogenetic spinal stimulation (OSS) as a less invasive and cell type-specific alternative to ISMS. To map forelimb muscle activation by OSS in rats, adeno-associated viruses (AAV) carrying the blue-light sensitive ion channels channelrhodopsin-2 (ChR2) and Chronos were injected into the cervical spinal cord at different depths and volumes. Following an AAV incubation period of several weeks, OSS-induced forelimb muscle activation and movements were assessed at 16 sites along the dorsal surface of the cervical spinal cord. Three distinct movement types were observed. We find that AAV injection volume and depth can be titrated to achieve OSS-based activation of several movements. Optical stimulation of the spinal cord is thus a promising method for dissecting the function of spinal circuitry and targeting therapies following injury. NEW & NOTEWORTHY Optogenetics in the spinal cord can be used both for therapeutic treatments and to uncover basic mechanisms of spinal cord physiology. For the first time, we describe the methodology and outcomes of optogenetic surface stimulation of the rat spinal cord. Specifically, we describe the evoked responses of forelimbs and address the effects of different adeno-associated virus injection paradigms. Additionally, we are the first to report on the limitations of light penetration through the rat spinal cord.

Laser-assisted delivery of synergistic combination chemotherapy in in vivo skin

The effectiveness of topical drugs for treatment of non-melanoma skin cancer is greatly reduced by insufficient penetration to deep skin layers. Ablative fractional lasers (AFLs) are known to enhance topical drug uptake by generating narrow microchannels through the skin, but information on AFL-drug delivery in in vivo conditions is limited. In this study, we examined pharmacokinetics, biodistribution and toxicity of two synergistic chemotherapy agents, cisplatin and 5-fluorouracil (5-FU), following AFL-assisted delivery alone or in combination in in vivo porcine skin. Detected at 0–120 h using mass spectrometry techniques, we demonstrated that fractional CO2 laser pretreatment (196 microchannels/cm2, 852 μm ablation depth) leads to rapid drug uptake in 1500 μm deep skin layers, with a sixfold enhancement in peak cisplatin concentrations versus non-laser-treated controls (5 h, P = 0.005). Similarly, maximum 5-FU deposition was measured within an hour of AFL-delivery, and exceeded peak deposition in non-laser-exposed skin that had undergone topical drug exposure for 5 days. Overall, this accelerated and deeper cutaneous drug uptake resulted in significantly increased inflammatory and histopathological effects. Based on clinical scores and transepidermal water loss measurement, AFL intensified local toxic responses to drugs delivered alone and in combination, while systemic drug exposure remained undetectable. Quantitative histopathologic analyses correspondingly revealed significantly reduced epidermal proliferation and greater cellular apoptosis after AFL-drug delivery; particularly after combined cisplatin + 5-FU exposure. In sum, by overcoming the primary limitation of topical drug penetration and providing accelerated, enhanced and deeper delivery, AFL-assisted combination chemotherapy may represent a promising treatment strategy for non-melanoma skin cancer.

Arginine Deprivation Therapy: Putative Strategy to Eradicate Glioblastoma Cells by Radiosensitization.

Tumor cells-even if nonauxotrophic-are often highly sensitive to arginine deficiency. We hypothesized that arginine deprivation therapy (ADT) if combined with irradiation could be a new treatment strategy for glioblastoma (GBM) patients because systemic ADT is independent of local penetration and diffusion limitations. A proof-of-principle in vitro study was performed with ADT being mimicked by application of recombinant human arginase or arginine-free diets. ADT inhibited two-dimensional (2-D) growth and cell-cycle progression, and reduced growth recovery after completion of treatment in four different GBM cell line models. Cells were less susceptible to ADT alone in the presence of citrulline and in a three-dimensional (3-D) environment. Migration and 3-D invasion were not unfavorably affected. However, ADT caused a significant radiosensitization that was more pronounced in a GBM cell model with p53 loss of function as compared with its p53-wildtype counterpart. The synergistic effect was independent of basic and induced argininosuccinate synthase or argininosuccinate lyase protein expression and not abrogated by the presence of citrulline. The radiosensitizing potential was maintained or even more distinguishable in a 3-D environment as verified in p53-knockdown and p53-wildtype U87-MG cells via a 60-day spheroid control probability assay. Although the underlying mechanism is still ambiguous, the observation of ADT-induced radiosensitization is of great clinical interest, in particular for patients with GBM showing high radioresistance and/or p53 loss of function. Mol Cancer Ther; 17(2); 393-406. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

Optimal Number, Location, and Size of Distributed Generators in Distribution Systems by Symbiotic Organism Search Based Method

This paper proposes an approach based on the Symbiotic Organism Search (SOS) for optimal determining sizing, siting, and number of Distributed Generations (DG) in distribution systems. The objective of the problem is to minimize the power loss of the system subject to the equality and inequality constraints such as power balance, bus voltage limits, DG capacity limits, and DG penetration limit. The SOS approach is defined as the symbiotic relationship observed between two organisms in an ecosystem, which does not need the control parameters like other meta-heuristic algorithms in the literature. For the implementation of the proposed method to the problem, an integrated approach of Loss Sensitivity Factor (LSF) is used to determine the optimal location for installation of DG units, and SOS is used to find the optimal size of DG units. The proposed method has been tested on IEEE 33-bus, 69-bus, and 118-bus radial distribution systems. The obtained results from the SOS algorithm have been compared to those of other methods in the literature. The simulated results have demonstrated that the proposed SOS method has a very good performance and effectiveness for the problem of optimal placement of DG units in distribution systems.

An adaptive geometry regulation strategy for 3D graphene materials: towards advanced hybrid photocatalysts.

Three-dimensional graphene (3DG) is promising for constructing monolithic photocatalysts for solar energy conversion. However, the structure-associated light-shielding effect and the intricate porous architecture of 3DG result in intrinsic limitations in light penetration and mass transfer over 3DG supported hybrids, which restricts their photocatalytic efficiency. Here, taking 3DG-organic hybrids as examples, we report a geometry regulation strategy to minimize such structural restrictions, which not only favors the interaction between light and the photoactive component, but also facilitates reactant adsorption over the 3DG-organic hybrids, thereby cooperatively boosting their photoactivity. Such an adaptive geometry regulation strategy is expected to guide the rational utilization of 3DG to construct high-performance hybrids for photoredox catalysis.

Octahedral molybdenum clusters as radiosensitizers for X-ray induced photodynamic therapy.

The use of radiosensitizers recently emerged as a promising approach to circumvent the depth penetration limitations of photodynamic therapy of cancer and to enhance radiotherapeutical effects. A widely explored current strategy is based on complex nanoarchitectures that facilitate the transfer of energy harvested from X-ray radiation by scintillating nanoparticles to the surrounding photosensitizer molecules to generate reactive oxygen species, mostly singlet oxygen O2(1Δg). We describe an alternative approach aiming at a considerable simplification of the architecture. The presented nanoparticles, made of the luminescent octahedral molybdenum cluster compound (n-Bu4N)2[Mo6I8(OCOCF3)6], efficiently absorb X-rays due to the high content of heavy elements, leading to the formation of the excited triplet states that interact with molecular oxygen to produce O2(1Δg). The activity of the nanoparticles on HeLa cells was first investigated under UVA/blue-light irradiation in order to prove the biological effects of photosensitized O2(1Δg); there is no dark toxicity at micromolar concentrations, but strong phototoxicity in the nanomolar range. The nanoparticles significantly enhance the antiproliferative effect of X-ray radiation in vitro at lower concentration than for previously reported O2(1Δg) radiosensitizing systems and this effect is more pronounced on cancer HeLa cells than non-cancer MRC cells. The results demonstrate that the cluster-based radiosensitizers of O2(1Δg) have strong potential with respect to the enhancement of the efficacy of radiotherapy with exciting opportunities for cancer treatment.

Effect of Overlay Structure for Cedar Board on Penetration Limit Energy of Ballistic Block

Effect of Overlay Structure for Cedar Board on Penetration Limit Energy of Ballistic Block

Rare-Earth-Doped Nanoparticles for Short-Wave Infrared Fluorescence Bioimaging and Molecular Targeting of αVβ3-Expressing Tumors.

The use of short-wave infrared (SWIR) light for fluorescence bioimaging offers the advantage of reduced photon scattering and improved tissue penetration compared to traditional shorter wavelength imaging approaches. While several nanomaterials have been shown capable of generating SWIR emissions, rare-earth-doped nanoparticles (REs) have emerged as an exceptionally bright and biocompatible class of SWIR emitters. Here, we demonstrate SWIR imaging of REs for several applications, including lymphatic mapping, real-time monitoring of probe biodistribution, and molecular targeting of the αvβ3 integrin in a tumor model. We further quantified the resolution and depth penetration limits of SWIR light emitted by REs in a customized imaging unit engineered for SWIR imaging of live small animals. Our results indicate that SWIR light has broad utility for preclinical biomedical imaging and demonstrates the potential for molecular imaging using targeted REs.

Bioactive nano-fibrous scaffold for vascularized craniofacial bone regeneration.

There has been a growing demand for bone grafts for correction of bone defects in complicated fractures or tumours in the craniofacial region. Soft flexible membrane like material that could be inserted into defect by less invasive approaches; promote osteoconductivity and act as a barrier to soft tissue in growth while promoting bone formation is an attractive option for this region. Electrospinning has recently emerged as one of the most promising techniques for fabrication of extracellular matrix such as nano-fibrous scaffolds that can serve as a template for bone formation. To overcome the limitation of cell penetration of electrospun scaffolds and improve on its osteoconductive nature, in this study, we fabricated a novel electrospun composite scaffold of polyvinyl alcohol (PVA)-poly (ε) caprolactone (PCL)-Hydroxyapatite based bioceramic (HAB), namely, PVA-PCL-HAB. The scaffold prepared by dual electrospinning of PVA and PCL with HAB overcomes reduced cell attachment associated with hydrophobic PCL by combination with a hydrophilic PVA and the HAB can contribute to enhance osteoconductivity. We characterized the physicochemical and biocompatibility properties of the new scaffold material. Our results indicate PVA-PCL-HAB scaffolds support attachment and growth of stromal stem cells; [human bone marrow skeletal (mesenchymal) stem cells and dental pulp stem cells]. In addition, the scaffold supported in vitro osteogenic differentiation and in vivo vascularized bone formation. Thus, PVA-PCL-HAB scaffold is a suitable potential material for therapeutic bone regeneration in dentistry and orthopaedics.

Adaptive planning approach for customer DG installations in smart distribution networks

The planning of active network management (ANM) schemes for distribution systems with distributed generation (DG) does not consider the random participation of customer-owned DGs. This study analyses and addresses the impact of the integration of customer-owned DG on the planning of ANM schemes and maximum DG penetration limits. The random customer DG installations are incorporated by considering sets of events where in each event the number, size and location of DG units are randomly generated. The events, in a set, are chronologically ordered and used to represent a possible scenario of customer-owned DG installations. A two-phase planning approach is proposed where the problem is formulated as a mixed-integer non-linear programming problem with an objective of determining the optimal ANM scheme for maximising the utility DG penetration considering customer DG installations. Several case studies are conducted on a generic 33 kV UK distribution network, including a comparison with the one-time planning approach. The results show that the optimal ANM scheme will vary with the number, locations and sizes of customer DGs and thus for utilities to achieve maximum DG penetration, it is recommended to adaptively control and equip DG units with the capability of switching between various ANM schemes.

Research on the characteristics of earthworm-like vibration drilling

The load transfer difficulty caused by borehole wall friction limits the rate of penetration (ROP) and extended-reach limit of complex structural well enormously. A new friction reduction technology called “earthworm-like drilling”, which can improve the load transfer and extended-reach limit, is proposed in this paper. A mathematical model based on “soft-string” model is developed to analysis the characteristics of this technology. Simulation results indicate that more stick-slip and load transfer issue are caused by higher friction. The earthworm-like drilling is more effective in reducing friction than single-point vibration drilling and less effective than multi-point vibration drilling because of the pulse pressure attenuation. However, this disadvantage can be offset by adding the number of axial oscillators. Amplitude and frequency of pulse pressure and the installation position of axial oscillators have great impact on the friction reduction and load transfer. An optimizing model based on projection gradient method is developed and used to optimize the position of three axial oscillators in a three-dimensional horizontal well. The weight on bit (WOB) increases significantly after the optimized position and the new position of axial oscillators move towards bottom of well and close to each other. Results verify the feasibility and advantages of earthworm-like drilling, and lay a solid theoretical foundation for its application in oil field drilling.

Comparison and combination of rotational imaging optical coherence tomography and selective plane illumination microscopy for embryonic study.

Several optical imaging techniques have been applied for high-resolution embryonic imaging using different contrast mechanisms, each with their own benefits and limitations. In this study, we imaged the same E9.5 mouse embryo with rotational imaging optical coherence tomography (RI-OCT) and selective plane illumination microscopy (SPIM). RI-OCT overcomes optical penetration limits of traditional OCT imaging that prohibit full-body imaging of mouse embryos at later stages by imaging the samples from multiple angles. SPIM enables high-resolution, 3D imaging with less phototoxicity and photobleaching than laser scanning confocal microscopy (LSCM) by illuminating the sample with a focused sheet of light. Side by side comparisons are supplemented with co-registered images. The results demonstrate that SPIM and RI-OCT are highly complementary and could provide more comprehensive tissue characterization for mouse embryonic research.

Constraint models of voltage fluctuation limit on OLTC/SVR caused by DG power fluctuation and generator disconnection to assess their impacts on DG penetration limit

With the rapid growth of distributed generation (DG) in distribution systems, DG penetration limit is becoming a more emergent issue. The short-term voltage fluctuation resulting from the DG power fluctuation of intermittent DG sources, e.g. photovoltaic (PV) and wind power, could trigger excessive actions of a transformer with on-load tap changer (OLTC) or a feeder step-voltage regulator (SVR). In addition, DG tripping from feeder will cause sudden large voltage step change. These facts limit the maximum allowable penetration of DG in distribution networks. This study proposes the constraint models of voltage fluctuation limit on OLTC/SVR resulting from DG power fluctuation and generator disconnection to assess their impacts on the DG penetration limit. A simple optimal power flow methodology is built according to the practical criteria and applied to the practical feeder systems, to demonstrate the huge advantages of the proposed constraint models in the assessment of DG penetration limit, which also validates that both factors have significant impacts on DG hosting capacity.