19,943 research outputs found
Virtual spring damper method for nonholonomic robotic swarm self-organization and leader following
In this paper, we demonstrate a method for self-organization and leader following of nonholonomic robotic swarm based on spring damper mesh. By self-organization of swarm robots we mean the emergence of order in a swarm as the result of interactions among the single robots. In other words the self-organization of swarm robots mimics some natural behavior of social animals like ants among others. The dynamics of two-wheel robot is derived, and a relation between virtual forces and robot control inputs is defined in order to establish stable swarm formation. Two cases of swarm control are analyzed. In the first case the swarm cohesion is achieved by virtual spring damper mesh connecting nearest neighboring robots without designated leader. In the second case we introduce a swarm leader interacting with nearest and second neighbors allowing the swarm to follow the leader. The paper ends with numeric simulation for performance evaluation of the proposed control method
Pleomorphic adenoma rehabilitative treatment in growing up patient: a 20-years follow-up
OBJECTIVE: Although tumors of minor salivary glands are rare, the pleomorphic adenoma is the most common pathology among the benign neoplasm and can be found with high prevalence in the junction between hard palate and soft palate. Most of the maxillary tumors are surgically treated through either a total or partial maxillectomy. However, surgical defects lead to both clinical and psychologic disorders for the patient. A postoperative obturator prosthesis is a good option in patients who underwent maxillectomy. It allows to restore both masticatory and speaking functions, as well as aesthetic appearance. When reconstruction of the surgical site is possible, an implant-supported prosthesis can be considered to guarantee a better function and aesthetic's rehabilitation. CASE REPORT: This clinical report presents the prosthetic rehabilitation of a patient who underwent maxillectomy because of a pleomorphic adenoma of hard palate minor salivary glands. The patient was treated with a palatal obturator prosthesis first and with an implant-supported prosthesis after surgical site's reconstruction and complete healing. CONCLUSIONS: The rehabilitation of the patient after maxillectomy through both these devices was an excellent option and provided clinical benefits, improving the patient's quality of life, allowing the patient's reinsertion into societ
New sizes of complete arcs in PG(2,q)
New upper bounds on the smallest size t_{2}(2,q) of a complete arc in the
projective plane PG(2,q) are obtained for 853<= q<= 2879 and q=3511,4096,
4523,5003,5347,5641,5843,6011. For q<= 2377 and q=2401,2417,2437, the relation
t_{2}(2,q)<4.5\sqrt{q} holds. The bounds are obtained by finding of new small
complete arcs with the help of computer search using randomized greedy
algorithms. Also new sizes of complete arcs are presented.Comment: 10 page
Instability of Boost-invariant hydrodynamics with a QCD inspired bulk viscosity
We solve the relativistic Navier-Stokes equations with homogeneous
boost-invariant boundary conditions, and perform a stability analysis of the
solution. We show that, if the bulk viscosity has a peak around as
inferred from QCD-based arguments, the background solution "freezes" at
to a nearly constant temperature state. This state is however highly unstable
with respect to certain inhomogeneous modes. Calculations show that these modes
have enough time to blow up and tear the system into droplets. We conjecture
that this is how freeze-out occurs in the QGP created in heavy ion collisions,
and perhaps similar transitions in the early universe.Comment: Accepted for publication, Rapid Communication in Physical Review C
Discussion extended, derivation and conclusions not change
Universal microstructure and mechanical stability of jammed packings
Jammed packings' mechanical properties depend sensitively on their detailed
local structure. Here we provide a complete characterization of the pair
correlation close to contact and of the force distribution of jammed
frictionless spheres. In particular we discover a set of new scaling relations
that connect the behavior of particles bearing small forces and those bearing
no force but that are almost in contact. By performing systematic
investigations for spatial dimensions d=3-10, in a wide density range and using
different preparation protocols, we show that these scalings are indeed
universal. We therefore establish clear milestones for the emergence of a
complete microscopic theory of jamming. This description is also crucial for
high-precision force experiments in granular systems.Comment: 11 pages, 7 figure
Monte Carlo Update for Chain Molecules: Biased Gaussian Steps in Torsional Space
We develop a new elementary move for simulations of polymer chains in torsion
angle space. The method is flexible and easy to implement. Tentative updates
are drawn from a (conformation-dependent) Gaussian distribution that favors
approximately local deformations of the chain. The degree of bias is controlled
by a parameter b. The method is tested on a reduced model protein with 54 amino
acids and the Ramachandran torsion angles as its only degrees of freedom, for
different b. Without excessive fine tuning, we find that the effective step
size can be increased by a factor of three compared to the unbiased b=0 case.
The method may be useful for kinetic studies, too.Comment: 14 pages, 4 figure
On sizes of complete arcs in PG(2,q)
New upper bounds on the smallest size t_{2}(2,q) of a complete arc in the
projective plane PG(2,q) are obtained for 853 <= q <= 4561 and q\in T1\cup T2
where T1={173,181,193,229,243,257,271,277,293,343,373,409,443,449,457,
461,463,467,479,487,491,499,529,563,569,571,577,587,593,599,601,607,613,617,619,631,
641,661,673,677,683,691, 709},
T2={4597,4703,4723,4733,4789,4799,4813,4831,5003,5347,5641,5843,6011,8192}.
From these new bounds it follows that for q <= 2593 and q=2693,2753, the
relation t_{2}(2,q) < 4.5\sqrt{q} holds. Also, for q <= 4561 we have t_{2}(2,q)
< 4.75\sqrt{q}. It is showed that for 23 <= q <= 4561 and q\in T2\cup
{2^{14},2^{15},2^{18}}, the inequality t_{2}(2,q) < \sqrt{q}ln^{0.75}q is true.
Moreover, the results obtained allow us to conjecture that this estimate holds
for all q >= 23. The new upper bounds are obtained by finding new small
complete arcs with the help of a computer search using randomized greedy
algorithms. Also new constructions of complete arcs are proposed. These
constructions form families of k-arcs in PG(2,q) containing arcs of all sizes k
in a region k_{min} <= k <= k_{max} where k_{min} is of order q/3 or q/4 while
k_{max} has order q/2. The completeness of the arcs obtained by the new
constructions is proved for q <= 1367 and 2003 <= q <= 2063. There is reason to
suppose that the arcs are complete for all q > 1367. New sizes of complete arcs
in PG(2,q) are presented for 169 <= q <= 349 and q=1013,2003.Comment: 27 pages, 4 figures, 5 table
Four-fold structure of vortex core states in Bi2Sr2CaCu2O8 (Bi2212)
We present a detailed study of vortex core spectroscopy in slightly overdoped
Bi2Sr2CaCu2O8 using a low temperature scanning tunneling microscope. Inside the
vortex core we observe a four-fold symmetric modulation of the local density of
states with an energy-independent period of (4.3\pm 0.3)a0. Furthermore we
demonstrate that this square modulation is related to the vortex core states
which are located at ~6 meV. Since the core-state energy is proportional to the
superconducting gap magnitude, our results strongly suggest the existence of a
direct relation between the superconducting state and the local electronic
modulations in the vortex core.Comment: 5 pages, 4 figures. Submitted to Physical Review Letter
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