2,856 research outputs found
Istraživanje savijanja čistih i hibridnih kompozitnih drvnih ploča uz pomoć Weibullove analize
The production of inexpensive wood products compared to their strength is important both in terms of economy and meeting the expectations of users. For this purpose, the use of hybrid wood products is increasing in the furniture industry. With the hybridization process, relatively cheap and flimsy material is combined with a material that has a stronger structure. Thus, stronger bonded material is manufactured cheaper. In this study, the flexural behavior of pure and hybrid wood composite panels, which were prepared by applying longitudinal jointing techniques from different wood materials, was investigated. In this context, pure chipboard, pure medium density fiberboard (MDF), chipboard-east beech and MDF-east beech hybrid wood composite panels were produced. During the hybridization process, oriental beech was combined by using the self-grooving technique in three different numbers as one row, two rows, and three rows. Flexural test results were analyzed according to the Weibull distribution method. The results of the analyses showed that the hybridization process increased the flexural strength and flexural modulus of pure wood panels by up to 214 %, and 95 %, respectively.Proizvodnja jeftinijih proizvoda od drva uz očuvanje njihove čvrstoće ima veliku važnost u ekonomskom smislu i u smislu ispunjavanja korisničkih očekivanja. Rezultat tog nastojanja jest sve veća uporaba hibridnih proizvoda od drva u industriji namještaja. Postupkom hibridizacije relativno jeftin i krhak materijal kombinira se s materijalom jače strukture te se na taj način postiže čvršći a jeftiniji materijal. U ovom je radu istraženo ponašanje čistih i hibridnih kompozitnih drvnih ploča pri savijanju, proizvedenih uzdužnim lijepljenjem različitoga drvnog materijala. Za potrebe istraživanja izrađene su čista ploča vlaknatica srednje gustoće (MDF) i hibridne kompozitne ploče od iverice i bukovine te od MDF ploče i bukovine. Tijekom postupka hibridizacije bukovi su elementi povezivani uz pomoć utora, a izrađeni su uzorci imali jedan, dva ili tri bukova elementa. Rezultati ispitivanja svojstava ploča pri savijanju analizirani su uz pomoć Weibullove distribucije. Pokazalo se da je postupak hibridizacije pridonio povećanju čvrstoće ploča na savijanje za 214 %, a modula elastičnosti za 95 %
VLSI Circuits for adaptive digital beamforming in ultrasound imaging
Cataloged from PDF version of article.For phased-array ultrasound imaging, alternative
beamforming techniques and their VLSI circuits are studied
to form a fully digital receive frontad hardware. In order
to increase the timiig accuracy in beamforming, a computationally
efficient interpolation scheme to increase the sampling
rate is examined. For adaptive beamforming, a phase aberration
correction method with very low computational complexity is
described. Image quality performance of the method is examined
by processing the non-aberrated and aberrated phased-array
experimental data sets of an ultrasound resolution phantom. A
digital beamforming scheme based on receive focusing at the
raster focal points is examined. The sector images of the resolution
phantom, reconstructed from the phased-array experimental
data by beamforming at the radial and raster focal points, are
presented for comparison of the image resolution performances
of the two beamforming schemes. VLSI circuits and their implementations
for the proposed techniques are presented
Direct Measure of Giant Magnetocaloric Entropy Contributions in Ni-Mn-In
Off-stoichiometric alloys based on Ni 2 MnIn have drawn attention due to the
coupled first order magnetic and structural transformations, and the large
magnetocaloric entropy associated with the transformations. Here we describe
calorimetric and magnetic studies of four compositions. The results provide a
direct measure of entropy changes contributions including at the first-order
phase transitions, and thereby a determination of the maximum field-induced
entropy change corresponding to the giant magnetocaloric effect. We find a
large excess entropy change, attributed to magneto-elastic coupling, but only
in compositions with no ferromagnetic order in the high-temperature austenite
phase. Furthermore, a molecular field model corresponding to antiferromagnetism
of the low-temperature phases is in good agreement, and nearly independent of
composition, despite significant differences in overall magnetic response of
these materials
Calorimetric and magnetic study for NiMnIn and relative cooling power in paramagnetic inverse magnetocaloric systems
The non-stoichiometric Heusler alloy NiMnIn undergoes a
martensitic phase transformation in the vicinity of 345 K, with the high
temperature austenite phase exhibiting paramagnetic rather than ferromagnetic
behavior, as shown in similar alloys with lower-temperature transformations.
Suitably prepared samples are shown to exhibit a sharp transformation, a
relatively small thermal hysteresis, and a large field-induced entropy change.
We analyzed the magnetocaloric behavior both through magnetization and direct
field-dependent calorimetry measurements. For measurements passing through the
first-order transformation, an improved method for heat-pulse relaxation
calorimetry was designed. The results provide a firm basis for the analytic
evaluation of field-induced entropy changes in related materials. An analysis
of the relative cooling power (RCP), based on the integrated field-induced
entropy change and magnetizing behavior of the Mn spin system with
ferromagnetic correlations, shows that a significant RCP may be obtained in
these materials by tuning the magnetic and structural transformation
temperatures through minor compositional changes or local order changes
The relationship between frontal sinus morphology and skeletal maturation
Background: The aim of this study is to evaluate the relationship between frontal sinus morphology and hand-wrist bone maturation by using postero-anterior (PA) cephalometric radiographs.Materials and methods: The study sample consisted of 220 patients divided into 11 groups based on the hand-wrist radiographs. The right and left maximum height, width and area of the frontal sinus parameters were measured in PA cephalometric radiographs of 220 subjects aged 8–18 years. The hand-wrist skeletal maturation stages were evaluated on the hand-wrist radiographs using the method of Fishman. The Kendall tau-b values were analysed to evaluate the correlation between the hand-wrist skeletal maturation stages and the frontalsinus parameters.Results: The right and left frontal sinus areas and widths were found to be larger in males than in females (p < 0.05). In males, a significant difference was observed in all frontal sinus parameters in different maturation stages (p < 0.001), while a statistically significant correlation was found in females between the left frontal sinus area, right frontal sinus height, right frontal sinus width and different maturation stages (p < 0.05).Conclusions: The relationship between frontal sinus dimensions obtained from PA cephalometric radiographs and hand-wrist maturation stages suggests that frontal sinuses can be used in determining growth and development
Capacity and delay scaling for broadcast transmission in highly mobile wireless networks
We study broadcast capacity and minimum delay scaling laws for highly mobile wireless networks, in which each node has to disseminate or broadcast packets to all other nodes in the network. In particular, we consider a cell partitioned network under the simplified independent and identically distributed (IID) mobility model, in which each node chooses a new cell at random every time slot. We derive scaling laws for broadcast capacity and minimum delay as a function of the cell size. We propose a simple first-come-first-serve (FCFS) flooding scheme that nearly achieves both capacity and minimum delay scaling. Our results show that high mobility does not improve broadcast capacity, and that both capacity and delay improve with increasing cell sizes. In contrast to what has been speculated in the literature we show that there is (nearly) no tradeoff between capacity and delay. Our analysis makes use of the theory of Markov Evolving Graphs (MEGs) and develops two new bounds on flooding time in MEGs by relaxing the previously required expander property assumption.National Science Foundation (U.S.) (Grant CNS-12170)National Science Foundation (U.S.) (Grant CNS-17137)National Science Foundation (U.S.) (Grant AST-15473
Speed limits in autonomous vehicular networks due to communication constraints
Autonomous vehicles need to be aware of other vehicles in their vicinity in order to avoid collisions and successfully perform their tasks. Such network awareness is ensured by exchanging location and control information over wireless radio channels. However, wireless interference constraints limit the number of messages that can be exchanged between the vehicles. In this paper, we study the impact of such communication constraints on maximum vehicle speed in dense autonomous vehicular networks. We define hazard rate to be the fraction of time a vehicle enters an `uncertainty region', i.e., a region where there is a positive probability of other vehicles being present due to lack of situational awareness. We show that the hazard rate follows a threshold behavior with respect to maximum speed v as the network density n increases to infinity. We show that for a 2D network the hazard rate tends to 1, if the maximum speed v decreases slower than n[superscript -3/2]; and tends to 0, if v decreases faster than n[superscript -3/2]. For the network hazard rate, which is the fraction of time any vehicle enters its uncertainty region, the threshold is n[superscript -2]. Finally, we extend these results to a 3D network and show that the thresholds for the 3D network are larger than in the 2D network
A phase aberration correction method for ultrasound imaging
Cataloged from PDF version of article.A computationally efficient method for phase aberration
correction in ultrasound imaging is presented. The method
is based on time delay estimation via minimization of the sum of
absolute differences between radio frequency samples of adjacent
array elements. Effects of averaging estimated aberration patterns
over scan angles, and truncation to a single bit wordlength
are examined. Phase distortions due to near-field inhomogeneities
are simulated using silicone rubber aberrators. Performance of
the method is tested using experimental data. Simulation studies
addressing different factors affecting efficiency of the method,
such as the number of iterations, window length, and the number
of scan angles used for averaging, are presented. Images of a
standard resolution phantom are reconstructed and used for
qualitative testing
Influence of missing array elements on phase aberration correction for medical ultrasound
Cataloged from PDF version of article.The influence of missing array elements on aberration correction based on time delay estimation using radio frequency signals of neighboring elements is experimentally investigated. Normalized cross correlation and sum of absolute differences are employed as the cost functions in aberration estimation. Their performance is tested through various measurements using radio frequency data acquired with a 3.3 MHz, 64-element phased array. Variation of cost functions and phase estimation error are obtained for different combinations of number of missing elements, amount of aberration, and noise level. For a particular combination of these parameters, a set of B-scan images is reconstructed and presented to examine the effects of residual phase errors on image quality
Sampling-based Algorithms for Optimal Motion Planning
During the last decade, sampling-based path planning algorithms, such as
Probabilistic RoadMaps (PRM) and Rapidly-exploring Random Trees (RRT), have
been shown to work well in practice and possess theoretical guarantees such as
probabilistic completeness. However, little effort has been devoted to the
formal analysis of the quality of the solution returned by such algorithms,
e.g., as a function of the number of samples. The purpose of this paper is to
fill this gap, by rigorously analyzing the asymptotic behavior of the cost of
the solution returned by stochastic sampling-based algorithms as the number of
samples increases. A number of negative results are provided, characterizing
existing algorithms, e.g., showing that, under mild technical conditions, the
cost of the solution returned by broadly used sampling-based algorithms
converges almost surely to a non-optimal value. The main contribution of the
paper is the introduction of new algorithms, namely, PRM* and RRT*, which are
provably asymptotically optimal, i.e., such that the cost of the returned
solution converges almost surely to the optimum. Moreover, it is shown that the
computational complexity of the new algorithms is within a constant factor of
that of their probabilistically complete (but not asymptotically optimal)
counterparts. The analysis in this paper hinges on novel connections between
stochastic sampling-based path planning algorithms and the theory of random
geometric graphs.Comment: 76 pages, 26 figures, to appear in International Journal of Robotics
Researc
- …