A composite grid-stiffened structure concept was selected for the payload fairing of the Minotaur launch vehicle. Compared to sandwich structures, this concept has an advantage of smaller manufacturing costs and lighter weight. To reduce weight the skin pockets are allowed to buckle visibly up to about 0.5 cm peak displacement.
Various failure modes were examined for the composite grid-stiffened structure. The controlling criterion for this design was a joint failure in tension between the ribs and skin of the structure. The identification of this failure mechanism and the assessment of bounding strains required to control it required extensive test and analysis effort. Increasing skin thickness to control skin buckling resulted in reduced strains between the skin and ribs.
Following the identification of the relevant failure criteria, a final design for the fairing was generated. The resulting 6 m tall fairing was constructed of a tow-placed carbon fiber composite grid structure that was over-wrapped to create a laminated skin. Upon completion of curing and machining, the fairing was cut in half to create the classic “clam-shell” fairing. Static qualification testing demonstrated the structural integrity of the fairing, thereby proving the design and manufacturing process. Loads were applied incrementally in a static loading scenario. The applied load envelope exceeded worst-case dynamic flight conditions with an added safety factor of 25%. At peak load the fairing maintained structural integrity while remaining within the required displacement envelope for payload safety.
Data were collected during the test from a variety of sensors including traditional displacement transducers and strain gages. In addition, full field displacement was monitored at critically loaded fairing sections by means of digital photogrammetry. This paper summarizes the test results, presents the overall performance of the fairing under the test loads, correlates test response and analysis, and identifies lessons learned.
Work continues at the Air Force Research Laboratory (AFRL) and Boeing to identify means of further controlling tensile failure of the un-reinforced polymer bonded joint between the ribs and skin. Stiffening of skin adjacent to the joints and introduction of lightweight foam jackets at the interior of the fairing both show promise of delaying joint failure to higher loads. 相似文献
Abstract— Defect‐free large‐area inorganic thick‐dielectric EL (TDEL) displays using Color by Blue (CBB) technology have been successfully developed. We have achieved the world's highest blue‐phosphor luminance of 900 cd/m2 for a single‐pixel device by using CBB and by optimizing the e‐beam gun configuration and the flow rate of H2S in the vacuum chamber. By analyzing the defects on panels with triple‐pattern phosphors and CBB panels, we also found that the number of defects on CBB panels can be drastically reduced compared with those on triple‐pattern panels. The defect‐free 17‐in. VGA CBB panels show better characteristics, a high peak luminance of 600 cd/m2 and a high contrast ratio of 1000:1, compared with those of triple‐pattern panels. 相似文献
We report a very simple, rapid and reproducible method for the fabrication of anisotropic silver nanostars (AgNS) that can be successfully used as highly efficient SERS substrates for different bioanalytes, even in the case of a near-infra-red (NIR) excitation laser. The nanostars have been synthesized using the chemical reduction of Ag+ ions by trisodium citrate. This is the first research reporting the synthesis of AgNS using only trisodium citrate as a reducing and stabilizing agent. The key elements of this original synthesis procedure are rapid hydrothermal synthesis of silver nanostars followed by a cooling down procedure by immersion in a water bath. The synthesis was performed in a sealed bottom flask homogenously heated and brought to a boil in a microwave oven. After 60 s, the colloidal solution was cooled down to room temperature by immersion in a water bath at 35 °C. The as-synthesized AgNS were washed by centrifugation and used for SERS analysis of test molecules (methylene blue) as well as biological analytes: pharmaceutical compounds with various Raman cross sections (doxorubicin, atenolol & metoprolol), cell lysates and amino acids (methionine & cysteine). UV-Vis absorption spectroscopy, (Scanning) Transmission Electron Microscopy ((S)TEM) and Atomic Force Microscopy (AFM) have been employed for investigating nanostars’ physical properties. 相似文献
Background: Severe outcomes of COVID-19 account for up to 15% of all cases. The study aims to check if any gene variants related to cardiovascular (CVD) and pulmonary diseases (PD) are correlated with a severe outcome of COVID-19 in a Polish cohort of COVID-19 patients. Methods: In this study, a subset of 747 samples from unrelated individuals collected across Poland in 2020 and 2021 was used and whole-genome sequencing was performed. Results: The GWAS analysis of SNPs and short indels located in genes related to CVD identified one variant significant in COVID-19 severe outcome in the HADHA gene, while for the PD gene panel, we found two significant variants in the DRC1 gene. In this study, both potentially protective and risk variants were identified, of which variants in the HADHA gene deserve the most attention. Conclusions: This is the first study reporting the association between the HADHA and DRC1 genetic variants and COVID-19 severe outcome based on the cohort WGS analysis. Although all the identified variants are localised in introns, they may be correlated and therefore inherited along with other risk variants, potentially causative to severe outcome of COVID-19 but not discovered yet. 相似文献
This study focuses on the use of genetic programming to automate the design of robust analog circuits. We define two complementary
types of failure modes: partial short-circuit and partial disconnect, and demonstrated novel circuits that are resilient across
a spectrum of fault levels. In particular, we focus on designs that are uniformly robust, and unlike designs based on redundancy,
do not have any single point of failure. We also explore the complementary problem of designing tamper-proof circuits that
are highly sensitive to any change or variation in their operating conditions. We find that the number of components remains
similar both for robust and standard circuits, suggesting that the robustness does not necessarily come at significant increased
circuit complexity. A number of fitness criteria, including surrogate models and co-evolution were used to accelerate the
evolutionary process. A variety of circuit types were tested, and the practicality of the generated solutions was verified
by physically constructing the circuits and testing their physical robustness. 相似文献
Cost‐efficient multi‐objective design optimization of antennas is presented. The framework exploits auxiliary data‐driven surrogates, a multi‐objective evolutionary algorithm for initial Pareto front identification, response correction techniques for design refinement, as well as generalized domain segmentation. The purpose of this last mechanism is to reduce the volume of the design space region that needs to be sampled in order to construct the surrogate model, and, consequently, limit the number of training data points required. The recently introduced segmentation concept is generalized here to allow for handling an arbitrary number of design objectives. Its operation is illustrated using an ultra‐wideband monopole optimized for best in‐band reflection, minimum gain variability, and minimum size. When compared with conventional surrogate‐based approach, segmentation leads to reduction of the initial Pareto identification cost by over 20%. Numerical results are supported by experimental validation of the selected Pareto‐optimal antenna designs. 相似文献
Current wind erosion and dust emission models neglect the heterogeneous nature of surface roughness and its geometric anisotropic effect on aerodynamic resistance, and over-estimate the erodible area by assuming it is not covered by roughness elements. We address these shortfalls with a new model which estimates aerodynamic roughness length (z0) using angular reflectance of a rough surface. The new model is proportional to the frontal area index, directional, and represents the geometric anisotropy of z0. The model explained most of the variation in two sets of wind tunnel measurements of aerodynamic roughness lengths (z0). Field estimates of z0 for varying wind directions were similar to predictions made by the new model. The model was used to estimate the erodible area exposed to abrasion by saltating particles. Vertically integrated horizontal flux (Fh) was calculated using the area not covered by non-erodible hemispheres; the approach embodied in dust emission models. Under the same model conditions, Fh estimated using the new model was up to 85% smaller than that using the conventional area not covered. These Fh simulations imply that wind erosion and dust emission models without geometric anisotropic sheltering of the surface, may considerably over-estimate Fh and hence the amount of dust emission. The new model provides a straightforward method to estimate aerodynamic resistance with the potential to improve the accuracy of wind erosion and dust emission models, a measure that can be retrieved using bi-directional reflectance models from angular satellite sensors, and an alternative to notoriously unreliable field estimates of z0 and their extrapolations across landform scales. 相似文献
The synthesis of nanoparticles from noble metals has received high attention from researchers due to their unique properties and their wide range of applications. Silver nanoparticles (AgNPs), in particular, show a remarkable inhibitory effect against microorganisms and viruses. Various methods have been developed to obtain AgNPs, however the stability of such nanostructures over time is still challenging. Researchers attempt to obtain particular shapes and sizes in order to tailor AgNPs properties for specific areas, such as biochemistry, biology, agriculture, electronics, medicine, and industry. The aim of this study was to design AgNPs with improved antimicrobial characteristics and stability. Two different wet chemical routes were considered: synthesis being performed (i) reduction method at room temperatures and (ii) solvothermal method at high temperature. Here, we show that the antimicrobial properties of the obtained AgNPs, are influenced by their synthesis route, which impact on the size and shape of the structures. This work analyses and compares the antimicrobial properties of the obtained AgNPs, based on their structure, sizes and morphologies which are influenced, in turn, not only by the type or quantities of precursors used but also by the temperature of the reaction. Generally, AgNPs obtained by solvothermal, at raised temperature, registered better antimicrobial activity as compared to NPs obtained by reduction method at room temperature. 相似文献
Reverse current in diodes can be dominated by generation processes, depending exponentially on temperature according to the
rate-limiting step in the generation process. In this report, the current-voltage-temperature (IVT) relationship is analyzed
for several midwave infrared and long-wave infrared (MWIR x = 0.295, LWIR x = 0.233) Hg1−xCdxTe (MCT) diodes. The energy varied from diode to diode. At high reverse biases, the energy tends toward the band gap energy.
Close to zero bias, the energy ranged from 0.06 to 0.1 eV. Deep level transient spectroscopy (DLTS) showed a broad peak centered
at 55–80 K for the MWIR MCT. Comparison of the DLTS spectrum to a simulation based on the energy and capture cross section
from a rate window analysis shows that the peak is a band of traps. The capacitance transient amplitude increased as the filling
pulse increased from 1 μs to 0.1 s, consistent with capture at a dislocation. A shift to lower temperatures for the peak was
also observed when the diodes are cooled under forward bias. The shift is reversible, indicating that the traps consist at
least partially of a bistable defect. 相似文献
A major issue in the design and operation of ad hoc networks is sharing the common spectrum among links in the same geographic
area. Bandwidth allocation, to optimize the performance of networks in which each station can converse with at most a single
neighbor at a time, has been recently studied in the context of Bluetooth Personal Area Networks. There, centralized and distributed,
capacity assignment heuristics were developed, with applicability to a variety of ad hoc networks. Yet, no guarantees on the
performance of these heuristics have been provided. In this paper, we extend these heuristics such that they can operate with
general convex objective functions. Then, we present our analytic results regarding these heuristics. Specifically, we show
that they are β-approximation (β<2) algorithms. Moreover, we show that even though the distributed and centralized algorithms
allocate capacity in a different manner, both algorithms converge to the same results. Finally, we present numerical results
that demonstrate the performance of the algorithms.
Randeep Bhatia received the Ph.D. degree in Computer Science from University of Maryland, the M.S. degree in Mathematics and Computer Science
from University of Illinois at Chicago and the B.Tech. degree in Computer Science and Engineering from Indian Institute of
Technology, Delhi. He is currently with the High Speed Networks Research Department at Bell Labs, Lucent technologies, working
on network design, traffic engineering and scheduling algorithms. His current research interests are in the area of QoS for
multimedia services in wireless data networks.
Adrian Segall received the B.Sc. and M.Sc. degrees in electrical engineering from the Technion, Israel Institute of Technology in 1965
and 1971, respectively, and the Ph.D. degree in electrical engineering with a minor in statistics from Stanford University
in 1973. After serving active duty in the Israel Defense Forces, he joined in 1968 the Scientific Department of Israel’s Ministry
of Defense. From 1973 to 1974 he was a Research Engineer at System Control Inc., Palo Alto, CA and a Lecturer at Stanford
University. From 1974 to 1976 he was an Assistant Professor of Electrical Engineering and Computer Science at the Massachusetts
Institute of Technology. From 1987 to 1998 he was on the faculty of the Department of Computer Science at the Technion. He
is presently Benjamin Professor of Computer-Communication Networks in the Department of Electrical Engineering, Technion,
Israel Institute of Technology. From 1982 to 1984 he was on leave with the IBM T.J.Watson Research Center, Yorktown Heights,
NY. He held visiting positions with IBM, AT&T and Lucent Bell Labs. His current research interests are in the area of optical
networks, wireless, sensor and ad-hoc networks. Dr. Segall is an IEEE Fellow and has served in the past as Editor for Computer
Communication Theory of the IEEE Transactions on Communications, Editor for the IEEE Information Theory Society Newsletter
and Senior Editor for the IEEE Journal on Selected Areas in Communications. He was selected as an IEEE delegate to the 1975
IEEE-USSR Information Theory Workshop, and is the recipient of the 1981 Miriam and Ray Klein Award for Outstanding Research
and of the 1990 Taub Award in Computer Science.
Gil Zussman received the B.Sc. degree in Industrial Engineering and Management and the B.A. degree in Economics (both summa cum laude) from the Technion—Israel Institute of Technology in 1995. He received the M.Sc. degree (summa cum laude) in Operations Research from Tel-Aviv University in 1999 and the Ph.D. degree in Electrical Engineering from the Technion—Israel
Institute of Technology in 2004. Between 1995 and 1998, he served as an engineer in the Israel Defense Forces. He is currently
a Postdoctoral Associate in the Laboratory for Information and Decision Systems in MIT. His current research interests are
in the area of ad hoc and sensor networks. In particular, he is interested in energy efficient protocols, medium access control
protocols, and personal area networks. Gil received the Knesset (Israeli Parliament) Award for distinguished students, the
Best Student Paper Award at the IFIP-TC6 Networking 2002 Conference, and the IEEE Communications Magazine Best Paper Award
at the OPNETWORK 2002 Conference. In 2004 he received the Marie Curie Outgoing International Fellowship and the Fulbright
Fellowship. 相似文献