101 research outputs found
Quantum Key Distribution over Probabilistic Quantum Repeaters
A feasible route towards implementing long-distance quantum key distribution
(QKD) systems relies on probabilistic schemes for entanglement distribution and
swapping as proposed in the work of Duan, Lukin, Cirac, and Zoller (DLCZ)
[Nature 414, 413 (2001)]. Here, we calculate the conditional throughput and
fidelity of entanglement for DLCZ quantum repeaters, by accounting for the DLCZ
self-purification property, in the presence of multiple excitations in the
ensemble memories as well as loss and other sources of inefficiency in the
channel and measurement modules. We then use our results to find the generation
rate of secure key bits for QKD systems that rely on DLCZ quantum repeaters. We
compare the key generation rate per logical memory employed in the two cases of
with and without a repeater node. We find the cross-over distance beyond which
the repeater system outperforms the non-repeater one. That provides us with the
optimum inter-node distancing in quantum repeater systems. We also find the
optimal excitation probability at which the QKD rate peaks. Such an optimum
probability, in most regimes of interest, is insensitive to the total distance.Comment: 12 pages, 6 figures; Fig. 5(a) is replace
Push recovery with stepping strategy based on time-projection control
In this paper, we present a simple control framework for on-line push
recovery with dynamic stepping properties. Due to relatively heavy legs in our
robot, we need to take swing dynamics into account and thus use a linear model
called 3LP which is composed of three pendulums to simulate swing and torso
dynamics. Based on 3LP equations, we formulate discrete LQR controllers and use
a particular time-projection method to adjust the next footstep location
on-line during the motion continuously. This adjustment, which is found based
on both pelvis and swing foot tracking errors, naturally takes the swing
dynamics into account. Suggested adjustments are added to the Cartesian 3LP
gaits and converted to joint-space trajectories through inverse kinematics.
Fixed and adaptive foot lift strategies also ensure enough ground clearance in
perturbed walking conditions. The proposed structure is robust, yet uses very
simple state estimation and basic position tracking. We rely on the physical
series elastic actuators to absorb impacts while introducing simple laws to
compensate their tracking bias. Extensive experiments demonstrate the
functionality of different control blocks and prove the effectiveness of
time-projection in extreme push recovery scenarios. We also show self-produced
and emergent walking gaits when the robot is subject to continuous dragging
forces. These gaits feature dynamic walking robustness due to relatively soft
springs in the ankles and avoiding any Zero Moment Point (ZMP) control in our
proposed architecture.Comment: 20 pages journal pape
Symmetry Method for Limit Cycle Walking of Legged Robots.
Dynamic steady-state walking or running gaits for legged robots correspond to periodic orbits in the dynamic model. The common method for obtaining such periodic orbits is conducting a numerical search for fixed points of a Poincare map. However, as the number of degrees of freedom of the robot grows, such numerical search becomes computationally expensive because in each search trial the dynamic equations need to be integrated. Moreover, the numerical search for periodic orbits is in general sensitive to model errors, and it remains to be seen if the periodic orbit which is the outcome of the search in the domain of the dynamic model corresponds to a periodic gait in the actual robot.
To overcome these issues, we have presented the Symmetry Method for Limit Cycle Walking, which relaxes the need to search for periodic orbits, and at the same time, the limit cycles obtained with this method are robust to model errors.
Mathematically, we describe the symmetry method in the context of so-called Symmetric Hybrid Systems, whose properties are discussed. In particular, it is shown that a symmetric hybrid system can have an infinite number of periodic orbits that can be identified easily. In addition, it is shown how control strategies need to be selected so that the resulting reduced order system still possesses the properties of a symmetric hybrid system.
The method of symmetry for limit cycle walking is successfully tested on a 12-DOF 3D model of the humanoid robot Romeo.PhDApplied and Interdisciplinary MathematicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133356/1/razavi_1.pd
Restricted Discrete Invariance and Self-Synchronization For Stable Walking of Bipedal Robots
Models of bipedal locomotion are hybrid, with a continuous component often
generated by a Lagrangian plus actuators, and a discrete component where leg
transfer takes place. The discrete component typically consists of a locally
embedded co-dimension one submanifold in the continuous state space of the
robot, called the switching surface, and a reset map that provides a new
initial condition when a solution of the continuous component intersects the
switching surface. The aim of this paper is to identify a low-dimensional
submanifold of the switching surface, which, when it can be rendered invariant
by the closed-loop dynamics, leads to asymptotically stable periodic gaits. The
paper begins this process by studying the well-known 3D Linear Inverted
Pendulum (LIP) model, where analytical results are much easier to obtain. A key
contribution here is the notion of \textit{self-synchronization}, which refers
to the periods of the pendular motions in the sagittal and frontal planes
tending to a common period. The notion of invariance resulting from the study
of the 3D LIP model is then extended to a 9-DOF 3D biped. A numerical study is
performed to illustrate that asymptotically stable walking may be obtained.Comment: Conferenc
Induced Myopia Secondary to Blunt Trauma
A 28-year-old young man presented with sudden and severe visual loss in the left eye, starting three days ago following blunt head trauma from a closed fist. Vision was not improved to better than 0.4 in the left eye. Slit lamp examinations revealed asymmetric anterior chamber depth (ACD) with shallow ACD in the left eye. The key learning in this report is the use of anterior segment optical coherence tomography (AS-OCT) to better document the anterior segment changes following the blunt trauma. AS-OCT was used to visualize the forward displacement of the iris-crystalline lens diaphragm secondary to ciliary body anterior rotation and ciliochoroidal effusion. There was a temporary myopic shift about 7.00D which resolved after 15 days
Frequency and characteristics of Brucellosis in Golestan Province, Iran
BACKGROUND: Brucellosis is a common widespread zoonotic disease between humans and livestock with significant economic and health problems caused by various species of Brucella. The disease is a significant public health issue throughout the world and one of the most socioeconomic problems in many developing countries. This study aimed to report the information available at the Provincial Health Center about the frequency and characteristics of patients with Brucellosis in Golestan Province, Iran.METHODS: This study was analytic-descriptive cross-sectional. The study population included all patients with Brucellosis diagnosed from 2011 to 2015 in the health center of Golestan Province, based on the serological method. The data gathering tool was a questionnaire that included demographic information, clinical presentation and examinations, history of exposure, laboratory findings, and treatment protocols. Descriptive statistics were reported as frequency and mean ± standard deviation (SD) and analyzed by SPSS software.RESULTS: In this study, a total of 1788 cases of Brucellosis were reported. The number of male cases was 1163 (65.04%) and female cases were 625 (34.95%). People who had a history of contact with infected animals were younger than the others. Musculoskeletal pain (79.69%) and fever (76.45%) were the most commonly reported clinical symptoms.CONCLUSION: Overall, the results indicate that Brucellosis is still a health problem in the province. The high incidence of Brucellosis in villages, the lack of full coverage of animal vaccination, and the link between the disease and livestock businesses are significant
Anticancer and Antitumor Potential of Fucoidan and Fucoxanthin, Two Main Metabolites Isolated from Brown Algae
Seaweed is one of the largest producers of biomass in marine environment and is a rich arsenal of active metabolites and functional ingredients with valuable beneficial health effects. Being a staple part of Asian cuisine, investigations on the crude extracts of Phaeophyceae or brown algae revealed marked antitumor activity, eliciting a variety of research to determine the active ingredients involved in this potential. The sulfated polysaccharide of fucoidan and carotenoid of fucoxanthin were found to be the most important active metabolites of brown algae as potential chemotherapeutic or chemopreventive agents. This review strives to provide detailed account of all current knowledge on the anticancer and antitumor activity of fucoidan and fucoxanthin as the two major metabolites isolated from brown algae
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