1,601 research outputs found
Self-Balancing Wheeled Robot for Discontinuous Terrains
Wheeled robots present an ideal platform for traversing even terrains, particularly due to their stable base and simple actuator design; however, many implementations are ill suited to handle abrupt changes in elevation. A common approach to this issue lies in the design of specialized members, either through a modified chassis, or in the geometry of the wheels. Unfortunately, such tactics either substantially increase the bulkiness of the robot or are too specialized to serve as a general solution. With the recent upsurge in interest for biologically inspired robots, the concept of a âhoppingâ robot could be pursued to answer this problem. Indeed, Ascento Robotics has already proven the feasibility of such a concept, and the increased agility sets this design apart from alternative solutions. This approach, however, is still relatively new and consequently costly, with Ascentoâs robots being leased by the hour in order to mitigate upfront costs. I propose a project to develop an open-source solution for the design of a self-balancing robot, capable of hopping across discontinuous surfaces. Through my efforts, I hope to set a framework that will support future projects in this field and to open the door for other universities interested in participating in collaborative research
Syn-kinematic hydration reactions, grain size reduction, and dissolution-precipitation creep in experimentally deformed plagioclase-pyroxene mixtures
Source at https://doi.org/10.5194/se-9-985-2018 .It is widely observed that mafic rocks are able to accommodate high strains by viscous flow. Yet, a number of questions concerning the exact nature of the involved deformation mechanisms continue to be debated. In this contribution, rock deformation experiments on four different water-added plagioclaseâpyroxene mixtures are presented:(i) plagioclase(An60â70)âclinopyroxeneâorthopyroxene,(ii) plagioclase(An60)âdiopside,(iii) plagioclase(An60)âenstatite,and iv) plagioclase(An01)âenstatite. Samples were deformed in general shear at strain rates of 3Ă10â5 to 3Ă10â6 sâ1, 800°C, and confining pressure of 1.0 or 1.5GPa. Results indicate that dissolutionâprecipitation creep (DPC) and grain boundary sliding (GBS) are the dominant deformation mechanisms and operate simultaneously. Coinciding with sample deformation, syn-kinematic mineral reactions yield abundant nucleation of new grains; the resulting intense gray size reduction is considered crucial for the activity of DPC and GBS. In high strain zones dominated by plagioclase, a weak, nonrandom, and geometrically consistent crystallographic preferred orientation (CPO) is observed. Usually, a CPO is considered a consequence of dislocation creep, but the experiments presented here demonstrate that a CPO can develop during DPC and GBS. This study provides new evidence for the importance of DPC and GBS in mid-crustal shear zones within mafic rocks, which has important implications for understanding and modeling mid-crustal rheology and flow
Mechanical Competence and Bone Quality Develop During Skeletal Growth.
Bone fracture risk is influenced by bone quality, which encompasses bone's composition as well as its multiscale organization and architecture. Aging and disease deteriorate bone quality, leading to reduced mechanical properties and higher fracture incidence. Largely unexplored is how bone quality and mechanical competence progress during longitudinal bone growth. Human femoral cortical bone was acquired from fetal (nâ=â1), infantile (nâ=â3), and 2- to 14-year-old cases (nâ=â4) at the mid-diaphysis. Bone quality was assessed in terms of bone structure, osteocyte characteristics, mineralization, and collagen orientation. The mechanical properties were investigated by measuring tensile deformation at multiple length scales via synchrotron X-ray diffraction. We find dramatic differences in mechanical resistance with age. Specifically, cortical bone in 2- to 14-year-old cases exhibits a 160% greater stiffness and 83% higher strength than fetal/infantile cases. The higher mechanical resistance of the 2- to 14-year-old cases is associated with advantageous bone quality, specifically higher bone volume fraction, better micronscale organization (woven versus lamellar), and higher mean mineralization compared with fetal/infantile cases. Our study reveals that bone quality is superior after remodeling/modeling processes convert the primary woven bone structure to lamellar bone. In this cohort of female children, the microstructural differences at the femoral diaphysis were apparent between the 1- to 2-year-old cases. Indeed, the lamellar bone in 2- to 14-year-old cases had a superior structural organization (collagen and osteocyte characteristics) and composition for resisting deformation and fracture than fetal/infantile bone. Mechanistically, the changes in bone quality during longitudinal bone growth lead to higher fracture resistance because collagen fibrils are better aligned to resist tensile forces, while elevated mean mineralization reinforces the collagen scaffold. Thus, our results reveal inherent weaknesses of the fetal/infantile skeleton signifying its inferior bone quality. These results have implications for pediatric fracture risk, as bone produced at ossification centers during children's longitudinal bone growth could display similarly weak points. © 2019 American Society for Bone and Mineral Research
Odderon and photon exchange in electroproduction of pseudoscalar mesons
We investigate the reaction where PS denotes a pseudoscalar
meson , or and X either a proton or resonance or
continuum states into which the proton can go by diffractive excitation. At
high energies photon and odderon exchange contribute to the reaction. The
photon exchange contribution is evaluated exactly using data for the total
virtual photon-proton absorption cross section. The odderon exchange
contribution is calculated in nonperturbative QCD, using functional integral
techniques and the model of the stochastic vacuum. For the proton we assume a
quark-diquark structure as suggested by the small odderon amplitude in and
forward scattering. We show that odderon exchange leads to a much
larger inelastic than elastic PS production cross section. Observation of our
reaction at HERA would establish the soft odderon as an exchange object on an
equal footing with the soft pomeron and would give us valuable insight into
both the nucleon structure and the mechanism of high energy diffractive
scattering.Comment: 20 pages, 7 figure
Masses and couplings of vector mesons from the pion electromagnetic, weak, and \pi\gamma transition form factors
We analyse the pion electromagnetic, charged-current, and
transition form factors at timelike momentum transfers ,
GeV, using a dispersion approach. We discuss in detail the propagator
matrix of the photon-vector-meson system and define certain reduced amplitudes,
or vertex functions, describing the coupling of this system to final states. We
then apply the derived analytic expressions to the analysis of the recent
, , and data. We find the reduced amplitudes for the coupling of the
photon and vector mesons to two pseudoscalars to be constant, independent of
, in the range considered, indicating a "freezing" of the amplitudes for
GeV. The fit to the form factor data leads to the following values of
the Breit-Wigner resonance masses m_{\rho^-}=775.3\pm 0.8 MeV,
m_{\rho^0}=773.7\pm 0.6 MeV and m_\omega=782.43\pm 0.05 MeV, where the errors
are only statistical.Comment: revtex, 23 page
Security of quantum bit string commitment depends on the information measure
Unconditionally secure non-relativistic bit commitment is known to be
impossible in both the classical and the quantum world. However, when
committing to a string of n bits at once, how far can we stretch the quantum
limits? In this letter, we introduce a framework of quantum schemes where Alice
commits a string of n bits to Bob, in such a way that she can only cheat on a
bits and Bob can learn at most b bits of information before the reveal phase.
Our results are two-fold: we show by an explicit construction that in the
traditional approach, where the reveal and guess probabilities form the
security criteria, no good schemes can exist: a+b is at least n. If, however,
we use a more liberal criterion of security, the accessible information, we
construct schemes where a=4 log n+O(1) and b=4, which is impossible
classically. Our findings significantly extend known no-go results for quantum
bit commitment.Comment: To appear in PRL. Short version of quant-ph/0504078, long version to
appear separately. Improved security definition and result, one new lemma
that may be of independent interest. v2: added funding reference, no other
change
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