BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//RLASKEY//CALENDEROUS//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180122T153358Z
DTSTART:20180129T160000Z
DTEND:20180129T170000Z
UID:event1886@bu.edu
URL:http://physics.bu.edu/events/show/1886
SUMMARY:"Buckling transition and antiferromagnetic liquids in two dimension
s"
DESCRIPTION:Featuring Danny Podolsky\, Technion\nHosted by: Anushya Chandra
n\n\nPart of the Condensed Matter Theory Seminar Series.\n\nCrystals of tra
pped ions are an example of ordered states of matter that emerge from the c
ompetition between kinetic energy and repulsive forces in confined volumes.
These systems can give us unique access to interesting questions in class
ical and quantum magnetism. For instance\, I will show that ions confined
to 2D undergo a buckling transition\, which is described by a six-state qua
ntum clock model. Motivated by this system\, I will discuss the melting of
2D antiferromagnets\, and will show that under certain conditions it is pos
sible to stabilize an antiferromagnetic liquid in two dimensions.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180130T152533Z
DTSTART:20180202T173000Z
DTEND:20180202T183000Z
UID:event1921@bu.edu
URL:http://physics.bu.edu/events/show/1921
SUMMARY:"Quantum Annealing to Solve 3-Regular 3-XORSAT on a Lattice"
DESCRIPTION:Featuring Pranay Patil \, Boston University\, Physics Departmen
t\n\nPart of the Condensed Matter Theory Seminar Series.\n\nHere we show ho
w we can embed the 3-regular 3-XORSAT on a square lattice made out of gates
which couple the bits in a manner that recreates the constraints. This sys
tem can be annealed to the solution by tuning a transverse field to zero. W
e explore ways to avoid two potential obstacles that limit how fast one can
anneal this system: 1) the nature of the phase transition as we tune the t
ransverse field and 2) the avoided level crossings for small transverse fie
ld strength. We discuss how the second pitfall can possibly be avoided in t
he lattice embedding. We also present Quantum Monte Carlo results on the na
ture of the phase transition for the embedding of XORSAT on the square latt
ice. We compare the results to the embedding on a random regular graph\, wh
ere the phase transition is known to be first order.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180208T195424Z
DTSTART:20180212T160000Z
DTEND:20180212T170000Z
UID:event1887@bu.edu
URL:http://physics.bu.edu/events/show/1887
SUMMARY:"Operator Spreading and the Quantum Butterfly Effect in Random Unit
ary Circuits"
DESCRIPTION:Featuring Sagar Vijay\, Massachusetts Institute of Technology\n
Hosted by: Philip Crowley\n\nPart of the Condensed Matter Theory Seminar Se
ries.\n\nWe provide universal\, long-distance descriptions for the ‘quant
um butterfly effect’\, which describes the spreading of a local disturban
ce in a quantum medium\, and is quantified by the ‘out-of-time-order corr
elator’ (OTOC). We obtain these results by studying quantum circuits mad
e of random unitaries\, which yield minimally structured models for chaotic
quantum dynamics\, and are able to capture universal properties of quantum
entanglement growth. In this setting\, we demonstrate a mapping between t
he OTOC and classical growth processes\, which leads to exact results and e
xplicit universal scaling forms for the OTOC. \nIn 1+1D\, we demonstrate th
at the OTOC satisfies a biased diffusion equation\, which gives exact resul
ts for its spatial profile\, and for the butterfly speed. In higher dimensi
ons\, we show that the averaged OTOC can be understood exactly via a corres
pondence with a classical droplet growth problem. We support our analytic a
rgument with simulations in 2+1D and demonstrate that in a lattice model\,
the late time shape of the spreading operator is in general not spherical.
However when full spatial rotational symmetry is present in 2+1D\, our mapp
ing implies an exact asymptotic form for the OTOC in terms of the Tracy-Wid
om distribution. For an alternative perspective on the OTOC in 1+1D\, we ma
p it to the partition function of an Ising-like model. As a result of speci
al structure arising from unitarity\, this partition function reduces to a
random walk calculation which can be performed exactly. We argue that the
coarse-grained pictures carry over to operator spreading in generic many-bo
dy systems.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180214T162949Z
DTSTART:20180216T170000Z
DTEND:20180216T180000Z
UID:event1924@bu.edu
URL:http://physics.bu.edu/events/show/1924
SUMMARY:Entanglement Spectrum in Quantum Many-Body Dynamics and Braiding of
Non-Abelian Anyons
DESCRIPTION:Featuring Zhicheng Yang \, Boston University\, Physics Departme
nt\n\nPart of the Condensed Matter Theory Seminar Series.\n\nWe study the e
ntanglement spectrum of highly entangled states in two different contexts:
(1) time evolved states after a quantum quench with Hamiltonians exhibiting
different dynamical phases; (2) braiding of non-abelian anyons capable or
not of universal quantum computation. In the first case\, we show that the
three distinct dynamical phases known as thermalization\, Anderson localiza
tion\, and many-body localization are marked by different patterns in the e
ntanglement spectrum after a quantum quench. While the entanglement spectru
m displays Poisson statistics for the case of Anderson localization\, it di
splays universal Wigner-Dyson statistics for both the cases of many-body lo
calization and thermalization\, albeit within very different time scales. W
e further show that the complexity of entanglement\, revealed by the possib
ility of disentangling the state through a Metropolis-like algorithm\, is s
ignaled by whether the entanglement spectrum is Poisson or Wigner-Dyson. In
the second part\, we study the entanglement spectrum of states generated o
ut of braiding two types of non-abelian anyons: the Majorana fermions and t
he Fibonacci anyons. We show that the information on whether certain repres
entations of the braid group associated with non-abelian anyons are capable
of universal quantum computation can also be extracted from the entangleme
nt spectrum.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180222T144758Z
DTSTART:20180223T170000Z
DTEND:20180223T180000Z
UID:event1930@bu.edu
URL:http://physics.bu.edu/events/show/1930
SUMMARY:"Draining a superfluid hose"
DESCRIPTION:Featuring Dries Sels\, Boston University\, Physics Department\n
\nPart of the Condensed Matter Theory Seminar Series.\n\nIn this talk I wil
l discuss ongoing work on the dynamics of quantum systems subject to contin
uous local measurement. Specifically\, I will discuss some preliminary resu
lts on 1D condensates in which particles are continuously being lost. In th
e thermodynamic limit\, a non-trivial non-equilibrium steady state will dev
elop. I will provide evidence for the fact that Hawking radiation is emitte
d from the drain.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180220T181233Z
DTSTART:20180226T160000Z
DTEND:20180226T170000Z
UID:event1897@bu.edu
URL:http://physics.bu.edu/events/show/1897
SUMMARY:"Physics of spin-orbit coupled wires in magnetic field: Majorana mo
des and Lifshitz transitions"
DESCRIPTION:Featuring Jay Sau\, University of Maryland\nHosted by: Anushya
Chandran\n\nPart of the Condensed Matter Theory Seminar Series.\n\nThe comb
ination of spin-orbit coupling and magnetic field produces an interesting b
andstructure with a co-existing Dirac point and Fermi points. In the first
part of my talk I will review how proximity-induced superconductivity is e
xpected to realize Majorana zero modes. I will discuss theoretical understa
nding of the results from the experimental search for Majorana zero modes i
n spin-orbit coupled semiconductor-based topological superconducting system
s. I will conclude this part discussing the possibility of interferometric
detection of topological superconducivity. \nIn the second part we discuss
strongly interacting Bosons subject to the same Hamiltonian\, which would b
e the Tonks gas version of the spin-orbit coupled gases realized in experim
ents. We use the effective Lagrangian formalism for classifying non-relativ
istic Nambu-Goldstone modes due to derive the existance of an Ising transit
ion between two gapless phases that can be thought of as a superfluid minim
ally coupled to an Ising gauge field. This coupling between the Ising model
and the superfluid turns out to modify the dynamical critical exponent fro
m Lorentz-like (z~1) to Lifshitz-like (z~2). We find these predictions to b
e consistent with DMRG simulations.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180301T140604Z
DTSTART:20180302T170000Z
DTEND:20180302T180000Z
UID:event1931@bu.edu
URL:http://physics.bu.edu/events/show/1931
SUMMARY:"Unbiased Markov chain Monte Carlo with couplings joint work with J
ohn O'Leary\, Yves F. Atchadé"
DESCRIPTION:Featuring Pierre E. Jacob\, Harvard University\n\nPart of the C
ondensed Matter Theory Seminar Series.\n\nMarkov chain Monte Carlo (MCMC) m
ethods provide consistent approximations of integrals as the number of iter
ations goes to infinity. MCMC estimators are generally biased after any fix
ed number of iterations\, which complicates both parallel computation and t
he construction of confidence intervals. We propose to remove this bias by
using couplings of Markov chains together with a telescopic sum argument of
Glynn & Rhee (2014). The resulting unbiased estimators can be computed in
parallel\, with confidence intervals following directly from the Central Li
mit Theorem for i.i.d. variables. We discuss practical couplings for popula
r algorithms such as Metropolis-Hastings\, Gibbs samplers\, and Hamiltonian
Monte Carlo. We establish the theoretical validity of the proposed estimat
ors and study their efficiency relative to the underlying MCMC algorithms.
Finally\, we illustrate the performance and limitations of the method on va
rious examples\, involving discrete and continuous high dimensional state s
paces.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180312T141548Z
DTSTART:20180319T150000Z
DTEND:20180319T170000Z
UID:event1933@bu.edu
URL:http://physics.bu.edu/events/show/1933
SUMMARY:"Quantum dimer models for high temperature superconductors"
DESCRIPTION:Featuring Garry Goldstein\, University of Cambridge\n\nPart of
the Condensed Matter Theory Seminar Series.\n\nIn this talk we review the s
lave boson meanﬁeld formulation of the fermion+boson quantum dimer model
for the pseudogap phase of the high temperature superconductors. We show th
at in the presence of weak slowly varying external magnetic and electric
elds the fermionic dimers undergo semiclassical motion in the external ﬁ
eld. As a result in the presence of magnetic ﬁelds strong enough to destr
oy superconductivity the dimers undergo quantum oscillations. Indeed they s
atisfy Onsager quantization for their orbits and Lifshtiz-Kosevich formula
for the amplitude of oscillations. We also compute the eﬀective charges o
f the dimers in the presence of external magnetic ﬁelds as a function of
temperature. We show that the eﬀective magnetic charge changes sign from
negative −e at low temperature to positive +e at high temperature. This l
eads to a change of the sign of the Hall coeﬃcient as a function of tempe
rature. We also compute the magnetoresistance as a function of the external
ﬁeld and temperature within a linearized Boltzmann equation approximatio
n for the fermionic dimers. Furthermore we further show that the dimers und
ergo a Lifshitz transition as a function of doping with a van Hove singular
ity appearing at the Fermi surface near optimal doping ∼ 20%. Indeed the
van Hove singularity leads to a divergence of the density of states and as
such an optimum Tc. We study the interplay of nematic ﬂuctuations and the
van Hove singularity both of which occur near optimal doping. We show that
the van Hove singularity modiﬁes the critical properties of the QCP (qua
ntum critical point) for nematic ﬂuctuations and that the QCP may be desc
ribed by Hertz Millis like theory with z = 4. This allows us to calculate t
he critical exponents of the nematic ﬂuctuations and to show that the fer
mionic dimers have non-Fermi liquid behavior near the QCP with the self ene
rgy diverging∼ ω3/4 near the QCP.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180322T171935Z
DTSTART:20180328T170000Z
DTEND:20180328T180000Z
UID:event1938@bu.edu
URL:http://physics.bu.edu/events/show/1938
SUMMARY:"Aspects of ETH in various systems"
DESCRIPTION:Featuring Mark Srednicki\, UCSB\n\nPart of the Condensed Matter
Theory Seminar Series.\n\nI will discuss the status of ETH in systems with
spontaneous symmetry breaking\,\nin large subsystems\, and in systems near
integrability.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180329T161936Z
DTSTART:20180402T150000Z
DTEND:20180402T160000Z
UID:event1899@bu.edu
URL:http://physics.bu.edu/events/show/1899
SUMMARY:"Chiral Phases in Frustrated 2D Antiferromagnets and Fractional Che
rn Insulators"
DESCRIPTION:Featuring Eduardo Fradkin\, University of Illinois at Urbana-Ch
ampaign \nHosted by: Christopher Laumann\n\nPart of the Condensed Matter Th
eory Seminar Series.\n\nThe problem of topological phases of matter is one
of the most fascinating open questions in theoretical physics. In this semi
nar I will discuss recent advances in the theory of topological phases in 2
D systems. A key tool for these studies is a lattice version of Chern-Simon
s gauge theory. In particular its application to the problem of chiral phas
es in magnetization plateaus of spin 1/2 quantum antiferromagnets on the Ka
gome lattice and of fractional Chern insulators. The role of topology in th
e effective field theory and fractionalization of translation symmetries wi
ll be discussed.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180404T143432Z
DTSTART:20180409T160000Z
DTEND:20180409T170000Z
UID:event1941@bu.edu
URL:http://physics.bu.edu/events/show/1941
SUMMARY:"Towards learning quantum states with generative models"
DESCRIPTION:Featuring Juan Felipe Carrasquilla\, Vector Institute for Arti
ficial Intelligence\nHosted by: Alexandre Day\n\nPart of the Condensed Matt
er Theory Seminar Series.\n\nThe technological success of machine learning
techniques has motivated a research area in the\ncondensed matter physics a
nd quantum information communities\, where new tools and conceptual connect
ions between\nmachine learning and many-body physics are rapidly developing
. In this talk\, I will discuss the use\nof generative models for learning
quantum states. First\, I will describe restricted Boltzmann machines\n(RBM
) as a tool to model the wave function of large many-body systems and explo
re their use in the\nproblem of quantum state tomography of pure states. In
the same vein\, I will briefly discuss how to learn\nmore general mixed st
ates through a combination of positive-operator valued measures\, tensor ne
tworks\,\nand generative models. In this setting\, generative models enable
accurate learning of prototypical quantum\nstates of large size directly f
rom measurements mimicking experimental data.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180413T135605Z
DTSTART:20180420T160000Z
DTEND:20180420T170000Z
UID:event1884@bu.edu
URL:http://physics.bu.edu/events/show/1884
SUMMARY:"Laplacian Growth"
DESCRIPTION:Featuring Mark Mineev-Weinstein\, Natal\nHosted by: Anatoli Pol
kovnikov\n\nPart of the Condensed Matter Theory Seminar Series.\n\nNumerous
unstable non-equilibrium physical processes produce a multitude of rich co
mplex patterns\, both compact and (more often) fractal. Shapes of patterns
in a long time limit include fingers in porous media\, dendritic trees in
crystallization\, fractals in bacterial colonies and malignant tissues\, ri
ver networks\, and other bio- and geo- systems. The patterns are often univ
ersal and reproducible. Geometry and dynamics of these forms present great
challenges\, because mathematical treatment of nonlinear\, non-equilibrium\
, dissipative\, and unstable dynamical systems is\, as a rule\, very diffic
ult\, if possible at all. While many impressive experimental and computati
onal results were accumulated\, powerful analytic methods for these systems
were very limited until recently. Remarkably\, many of these growth proces
ses were reduced (after some idealization) to a mathematical formulation\,
which owns rich\, powerful and beautiful integrable structure\, and reveals
deep connections with other exact disciplines\, lying far from non-equilib
rium growth. In physics the examples include quantum gravity\, quantum Hall
effect\, and phase transitions. In classical mathematics\, this structure
was found to be deeply interconnected with such fields as the inverse poten
tial problem\, classical moments\, orthogonal polynomials\, complex analysi
s\, and algebraic geometry. In modern mathematical physics we established t
ight relations of nonlinear growth to integrable hierarchies and deformatio
ns\, normal random matrices\, stochastic growth\, and conformal theory. Thi
s mathematical structure made possible to see many outstanding problems in
a new light and solve several long-standing challenges in pattern formation
and in mathematical physics.\n\nDuring the talk I will provide brief histo
ry with key experiments and paradigms in the field\, make short surveys of
mathematics mentioned above\, expose the integrable structure hidden behind
the interface dynamics\, and will present major results up to date in this
rapidly growing field.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180423T130848Z
DTSTART:20180423T150000Z
DTEND:20180423T160000Z
UID:event1946@bu.edu
URL:http://physics.bu.edu/events/show/1946
SUMMARY:"Monopole harmonic superconductivity"
DESCRIPTION:Featuring Yi Li\, Johns Hopkins University\nHosted by: Anushya
Chandran\n\nPart of the Condensed Matter Theory Seminar Series.\n\nIn this
talk\, I will present a dramatic effect of Fermi surface monopole structure
on superconducting pairing symmetry: When Cooper pairs acquire non-trivial
two-particle Berry phases\, their pairing phases cannot be globally well-d
efined in the momentum space. Therefore\, the conventional description of s
uperconducting pairing symmetries in terms of spherical harmonics (e.g. s-\
, p-\, d-waves) ceases to apply. Instead\, they are represented by monopole
harmonic functions. These novel superconducting states can be realized in
doped Weyl semi-metals. They exhibit topologically protected nodal gap func
tions and rich patterns of Majorana surface arcs regardless of concrete pai
ring mechanism.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180427T152913Z
DTSTART:20180427T163000Z
DTEND:20180427T173000Z
UID:event1885@bu.edu
URL:http://physics.bu.edu/events/show/1885
SUMMARY:CM Friday Seminar TBA
DESCRIPTION:Featuring Ivan Schuller\, University of California\, Santa Barb
ara\nHosted by: Kevin Smith\n\nPart of the Condensed Matter Theory Seminar
Series.\n\n
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CANCELLED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180425T154207Z
DTSTART:20180430T150000Z
DTEND:20180430T160000Z
UID:event1947@bu.edu
URL:http://physics.bu.edu/events/show/1947
SUMMARY:"Status of the Search for Majorana Fermions in Semiconductor Nanowi
res"
DESCRIPTION:Featuring Sergey Frolov\, University of Pittsburgh\nHosted by:
Alexander Sushkov\n\nPart of the Condensed Matter Theory Seminar Series.\n\
nTunneling spectroscopy measurements on one-dimensional superconducting hyb
rid materials have revealed signatures of Majorana fermions which are the e
dge states of a bulk topological superconducting phase. We couple strong sp
in-orbit semiconductor InSb nanowires to conventional superconductors (NbTi
N\, Al) to obtain additional signatures of Majorana fermions and to explore
the topological phase transition. A potent alternative explanation for ma
ny of the recent experimental Majorana reports is that a non-topological An
dreev state localizes near the end of a nanowire. We compare Andreev and Ma
jorana modes and investigate ways to clearly distinguish the two phenomena.
We are also exploring how Andreev states can be chained together along the
nanowire to realize the one-dimensional Kitaev model\, a discrete way of g
enerating Majorana modes.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20180525T031943Z
LAST-MODIFIED:20180507T190418Z
DTSTART:20180511T160000Z
DTEND:20180511T170000Z
UID:event1948@bu.edu
URL:http://physics.bu.edu/events/show/1948
SUMMARY:"Fate of Orthogonality Catastrophe in driven-open quantum systems"
DESCRIPTION:Featuring Federico Tonielli\, University of Cologne\, Germany\n
Hosted by: Anatoli Polkovnikov\n\nPart of the Condensed Matter Theory Semin
ar Series.\n\nOrthogonality Catastrophe is a paragon of the dramatic effect
s provoked by the interaction of a gapless quantum many body system with an
impurity. Its instance in real time dynamics is a universal\, algebraic de
cay of the fidelity between the unperturbed ground state and the ground sta
te evolved in the presence of the impurity itself.\n\nWe consider the case
of a quantum system subject to a local dephasing channel\, i.e. locally int
eracting with an external Markovian bath\, that plays the role of a new typ
e of impurity and whose dynamics is well described by a local Lindblad quan
tum master equation. We find in this new context\, a novel\, universal\, ti
me-resolved scaling behavior of the fidelity\, that counteracts the exponen
tial decay due to heating\, unlike the case of unitary dynamics.\n\nThe fir
st model we consider is the one-dimensional quantum Ising chain in transver
se field with spin dephasing\, where we establish this novel character for
the fidelity by means of a resummation of the perturbative expansion.\n\nWe
further investigate the phenomenon in a quantum field theory of free boson
s subject to a stochastic impurity potential\, localized in space but rando
m in time\, constructing a functional integral expression for the fidelity.
The latter is computed for linear and quadratic impurity potentials\, and
for impurities with short correlations in time. An intriguing crossover to
the familiar OC is found in the limit of infinite correlation time of the i
mpurity\, for which a physical picture is proposed. \nFinally\, we ague how
to detect the phenomenon through direct measurement of an accessible obser
vable in cold atoms experiments.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR