BEGIN:VCALENDAR
PRODID:-//PSU Mathematics Department//Seminar iCalendar Generator//EN
VERSION:2.0
CALSCALE:GREGORIAN
METHOD:PUBLISH
X-WR-CALNAME:Geometry Luncheon Seminar
X-WR-TIMEZONE:America/New_York
BEGIN:VTIMEZONE
TZID:America/New_York
X-LIC-LOCATION:America/New_York
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150114T120500
DTEND;TZID=America/New_York:20150114T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25462
SUMMARY:Geometry Luncheon Seminar - TBA
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: TBA\nAbstract Link:
http://
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150121T120500
DTEND;TZID=America/New_York:20150121T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25463
SUMMARY:Geometry Luncheon Seminar - Closed orbits of pseudo-Anosov flows: c
ardinality and length growth
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: Closed orbits of pse
udo-Anosov flows: cardinality and length growth\nSpeaker: Sergio Fenley\,
Florida State University\nAbstract: There are Anosov and pseudo-Anosov fl
ows so that some orbitsare freely homotopic to infinitely many other orbit
s. Given such an infinite free homotopy class we analyse its interaction w
ith the torus\ndecomposition of the manifold: whether they can all be cont
ained in a Seifert piece or atoroidal piece. There is a natural ordering o
f an infinite subset of such a collection\, indexed as (gamma_i). We analy
se the growth of the length of gamma_i as a function of i.We obtain some i
nequalities which have some ergodic theory consequences.\n\nThis is a join
t work with Thomas Barthelme.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150128T120500
DTEND;TZID=America/New_York:20150128T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25464
SUMMARY:Geometry Luncheon Seminar - Variational principles for isometric em
beddings and rigidity
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: Variational principl
es for isometric embeddings and rigidity\nSpeaker: Ivan Izmestiev\, FU Ber
lin (Visiting Penn State)\nAbstract: The discrete total scalar curvature o
f a manifold glued from euclidean (or hyperbolic) simplices is the sum of
the lengths of edges multiplied with the angular defects around them (a vo
lume term is added in the hyperbolic case). This functional has very nice
variational properties with respect to the length variables: its critical
points correspond to vanishing angle defects\, that is to constant curvatu
re metrics. In certain cases we are able to determine the signature of its
second variation\, which looks very much like that of its smooth counterp
art. We will present some applications to isometric embeddings and rigidit
y.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150204T120500
DTEND;TZID=America/New_York:20150204T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25465
SUMMARY:Geometry Luncheon Seminar - LATE Lunch Seminar: 2:30 (unusual time
\, but food will be catered).
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: LATE Lunch Seminar:
2:30 (unusual time\, but food will be catered).\nSpeaker: Charlie Epstein
\, UPenn\nAbstract: I will speak on "Analytic Foundations for Kimura Diffu
sion Equations"\nAbstract: We discuss the analysis of a class of degenerat
e elliptic operators defined on manifolds with corners\, which arise in Po
pulation Biology. Using techniques pioneered by J. Moser\, and extended an
d refined by L. Saloff-Coste\, Grigorâ€™yan\, and Sturm\, we show that wea
k solutions to the parabolic problem defined by a sub-class of these opera
tors\, which consists of those that can be defined by Dirichlet forms and
have non- vanishing transverse vector field\, satisfy a Harnack inequality
. This allows us to conclude that the solutions to these equations belong
\, for positive times\, to the natural anisotropic Holder spaces\, and als
o leads to upper and\, in some cases\, lower bounds for the heat kernels o
f these operators.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150211T120500
DTEND;TZID=America/New_York:20150211T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25466
SUMMARY:Geometry Luncheon Seminar - TBA
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: TBA\nAbstract Link:
http://
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150218T120500
DTEND;TZID=America/New_York:20150218T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25467
SUMMARY:Geometry Luncheon Seminar - Local topology and geometry of orbifold
s
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: Local topology and g
eometry of orbifolds\nSpeaker: Christian Lange\, University of Cologne\nAb
stract: We will discuss variants of the following question:When is the quo
tient of R^n by a finite linear group a manifold?
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150225T120500
DTEND;TZID=America/New_York:20150225T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25468
SUMMARY:Geometry Luncheon Seminar - TBA
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: TBA\nAbstract Link:
http://
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150304T120500
DTEND;TZID=America/New_York:20150304T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25469
SUMMARY:Geometry Luncheon Seminar - Geodesics on the convex surfaces.
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: Geodesics on the con
vex surfaces.\nSpeaker: Anton Petrunin\, Penn State\nAbstract: We give a u
niversal bound for the variation of turn of minimizing geodesics on convex
surfaces. This is a joint work with Nina Lebedeva.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150311T120500
DTEND;TZID=America/New_York:20150311T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25470
SUMMARY:Geometry Luncheon Seminar - TBA
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: TBA\nAbstract Link:
http://
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150318T120500
DTEND;TZID=America/New_York:20150318T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25471
SUMMARY:Geometry Luncheon Seminar - TBA
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: TBA\nAbstract Link:
http://
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150325T120500
DTEND;TZID=America/New_York:20150325T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25472
SUMMARY:Geometry Luncheon Seminar - Geodesics on convex surfaces.
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: Geodesics on convex
surfaces.\nSpeaker: Anton Petrunin\, Penn State\nAbstract: We give a unive
rsal bound for the variation of turn of minimizing geodesics on convex sur
faces. This is a joint work with Nina Lebedeva.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150401T120500
DTEND;TZID=America/New_York:20150401T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25473
SUMMARY:Geometry Luncheon Seminar - A Fary-Milnor theorem for CAT(0) spaces
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: A Fary-Milnor theore
m for CAT(0) spaces\nSpeaker: Stephan Stadler\, University of Cologne\nAbs
tract: We prove the following CAT(0) version of Fary-Milnor's theorem on k
nots. If $\\gamma$ is a Jordan curve of total curvature $\\leq4\\pi$ in a
CAT(0) space\, then either $\\gamma$ spans an embedded disc or else the to
tal curvature of $\\gamma$ equals $4\\pi$ and $\\gamma$ bounds a star shap
ed subset intrinsically isometric to a Euclidean cone of cone angle equal
to $4\\pi$.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150408T120500
DTEND;TZID=America/New_York:20150408T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25474
SUMMARY:Geometry Luncheon Seminar - Interpolation of Riemannian manifolds
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: Interpolation of Rie
mannian manifolds\nSpeaker: Sergei Ivanov\, Steklov Institute and SPb Univ
ersity\, visiting PSU\nAbstract: Given a discrete metric space\, how can o
ne determine whether it approximates a Riemannian manifold with prescribed
bounds for curvature and injectivity radius? I will discuss a solution of
this problem and some related topics from geometry and analysis.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150415T120500
DTEND;TZID=America/New_York:20150415T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25475
SUMMARY:Geometry Luncheon Seminar - Exceptional Jordan algebras and the Lee
ch lattice
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: Exceptional Jordan a
lgebras and the Leech lattice\nSpeaker: John Baez\, University of Californ
ia (Host: John Roe)\nAbstract: When Jordan\, Wigner and von Neumann classi
fied algebras of observables in their work on the foundations of quantum m
echanics\, they found 4 infinite series and one exception. This 'exceptio
nal Jordan algebra' is 27-dimensional and consists of 3x3 self-adjoint oct
onionic matrices. The Leech lattice is another exceptional structure: the
unique 24-dimensional even unimodular lattice with no vectors of length s
quared 2. I'll explain these entities and describe some work with Greg Eg
an where we made the Leech lattice into a 'Jordan subring' of the exceptio
nal Jordan algebra.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150422T120500
DTEND;TZID=America/New_York:20150422T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25476
SUMMARY:Geometry Luncheon Seminar - Positive entropy arises between KAM tor
i
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: Positive entropy ari
ses between KAM tori\nSpeaker: Dong Chen\, Penn State\nAbstract: According
to KAM theory\, given an integrable system\, after making a small perturb
ation\, we still have invariant tori under the perturbed system. What happ
ens between these KAM tori attracts lots of attention. In this talk I will
present a project in work in order to find a perturbed hamiltonian flow o
n the cotangent bundle of 2-torus with positive metric entropy\, which unv
eils some type of complexity between KAM tori.
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150429T120500
DTEND;TZID=America/New_York:20150429T132000
LOCATION:MB114
URL:http://www.math.psu.edu/seminars/meeting.php?id=25477
SUMMARY:Geometry Luncheon Seminar - The classification of Clustering Scheme
s
DESCRIPTION:Seminar: Geometry Luncheon Seminar\nTitle: The classification o
f Clustering Schemes\nSpeaker: Facundo Memoli\, Ohio State U.\nAbstract: C
lustering is a fundamental task in the analysis of data. There are hundred
s of different clustering methods being used by practitioners but there is
little agreement on which methods are better or even applicable in differ
ent scenarios. One possibility first proposed by Kleinberg is to formulate
some desirable properties or axioms that clustering methods should satisf
y. Kleinberg studies flat clustering\, that is the assignment of partition
s to finite metric spaces\, under three axioms: surjectivity\, scale invar
iance\, and one additional property he called 'consistency'. Consistency c
an roughly be translated into requiring that the clustering method be a fu
nctor from the category of finite metric spaces (with 1-Lipschitz maps as
morphisms) into the category of partitioned sets (with refinement as mor
phisms). He proves that there exists no method that can satisfy the three
axioms simultaneously. \n\nTogether with G.Carlsson we proved that if inst
ead we study hierarchical clustering methods -- that is methods that take
a finite metric space and output a nested collection of partitions -- then
there exists a unique method satisfying conditions similar to Kleinberg's
. In the course of our study of clustering methods we have identified othe
r properties that appear to be of interest: representability and excisiven
ess. We have some results about the classification of methods satisfying t
hose. We have also studied the problem of clustering networks: weighted di
rected dissimilarity graphs. We found that this is a much richer scenario
in which our uniqueness result becomes a bounding statement: all possible
methods lie (in an appropriate sense) between two methods which happen to
coalesce when the networks are symmetric.
END:VEVENT
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