Higgs Boson Search Webcast

Craig Blocker writes:

The Higgs boson has been sought for many years by high energy physics experiments.  It is the only particle in the standard model of particle physics that has not yet been observed and plays a crucial role since it gives mass to the other fundamental particles.

Tomorrow at 8:00 am EST (Tues., Dec. 13), CERN is giving a seminar (webcast) about the status of the search for the Higgs at the LHC by the two general purpose detector collaborations, ATLAS and CMS.  Although the data is not quite strong enough yet to claim a discovery, the evidence is becoming strong.

The Physics Department will show a web cast of this seminar in Abelson 131. The Brandeis high energy group has been a member of the ATLAS experiment for many years and has been instrumental in building parts of the detector that are key to this measurement.  I will be there to answer any questions.

Although it is early in the morning for most, if you are interested, please come to what should be a very interesting talk.


Eisenbud Lectures: “The Mathematics of Dynamic Random Networks”

This year’s Eisenbud Lectures in Mathematics and Physics will be given by Dr. Jennifer Chayes, Distinguished Scientist and Managing Director of Microsoft Research New England. Dr. Chayes is well known for her work on the phase transitions in combinatorial and computer science problems; she is a world expert on the study of random, dynamically growing graphs, which can be used to model real-world social and technological networks.

Dr. Chayes received her PhD in mathematical physics from Princeton.  After postdoctoral fellowships at Harvard and Cornell, she was on the faculty at UC Los Angeles before co-founding the theory group at Microsoft Research in Redmond, Washington.  In 2008 she co-founded Microsoft Research New England. She is a fellow of the American Association for the Advancement of Science, the Fields Institute, and the Association for Computing Machinery; she is also a National Associate of the National Academies.

The Eisenbud Lectures are the result of a generous donation by Leonard and Ruth-Jean Eisenbud, intended for a yearly set of lectures by an eminent physicist or mathematician working close to the interface of the two subjects. Dr. Chayes’ distinguished career working on fundamental issues in mathematics, physics, and computer science makes her an ideal speaker for this series.

The lectures will take place at 4 PM on Tuesday Nov. 29 and at 4:30 PM on Thursday Dec. 1. both in Abelson 131.  A full description of the lectures can be found below. Driving directions, maps, links to the MBTA, and so forth can be found at: http://www.brandeis.edu/about/visiting/directions.html.  If you need parking, please contact Catherine Broderick at cbroderi@brandeis.edu.  A reception will be held after the first lecture on Tuesday November 29th from 5pm – 7pm in the Faculty Club Lounge at Brandeis.  All are welcome.

Everybody should come out to hear this year’s lectures!  They promise to be a lot of fun.

During the past decade, dynamic random networks have become increasingly important in communication and information technology.  Vast, self-engineered networks, like the Internet, the World Wide Web, and online social networks, have facilitated the flow of information, and served as media for social and economic interaction.  I will discuss both the mathematical challenges and opportunities that exist in describing these networks:  How do we model these networks – taking into account both observed features and incentives?  What processes occur on these networks, again motivated by strategic interactions and incentives, and how can we influence or control these processes?  What algorithms can we construct on these networks to make them more valuable to the participants?  In this talk, I will review the general classes of mathematical problems which arise on these networks, and present a few results which take into account mathematical, computer science and economic considerations.  I will also present a general theory of limits of sequences of networks, and discuss what this theory may tell us about dynamically growing networks.

LECTURE 1:  Models and Behavior of the Internet,  the World Wide Web and Online Social Networks
Although the Internet, the World Wide Web and online social networks have many distinct features, all have a self-organized structure, rather than the engineered architecture of previous networks, such as phone or transportation systems.  As a consequence of this self-organization, these networks have a host of properties which differ from those encountered in engineered structures:  a broad “power-law” distribution of connections (so-called “scale-invariance”), short paths between two given points (so-called “small world phenomena” like “six degrees of separation”), strong clustering (leading to so-called “communities and subcultures”), robustness to random errors, but vulnerability to malicious attack, etc.    During this lecture, I will first review some of the distinguishing observed features of these networks, and then discuss some of the models which have been devised to explain these features.  I will also discuss processes and algorithms on these networks, focusing on a few particular examples.

LECTURE 2:  Convergent Sequences of Networks
In the second lecture of this series, I will abstract some of the lessons of the first lecture.  Inspired by dynamically growing networks, I will ask how we can characterize general sequences of graphs in which the number of nodes grows without bound.   In particular, I will define various natural notions of convergence for a sequence of graphs, and show that, in the case of dense graphs and even some sparse graphs, many of these notions are equivalent.  I will also give a construction for a function representing the limit of a sequence of graphs.  I’ll review examples of some simple growing network models, and illustrate the corresponding limit functions.  I will also discuss the relationship between these convergent sequences and some notions from mathematical statistical physics.

Dynamics of double-strand break repair

In a new paper in the journal Genetics, former Brandeis postdoc Eric Coïc and undergrads Taehyun Ryu and Sue Yen Tay from Professor of Biology Jim Haber’s lab, along with grad student Joshua Martin and Professor of Physics Jané Kondev, tackle the problem of understanding the dynamics of homologous recombination after double strand breaks in yeast. According to Haber,

The accurate repair of chromosome breaks is an essential process that prevents cells from undergoing gross chromosomal rearrangements that are the hallmark of most cancer cells.  We know a lot about how such breaks are repaired.  The ends of the break are resected and provide a platform for the assembly of many copies of the key recombination protein, Rad51.  Somehow the Rad51 filament is then able to facilitate a search of the entire DNA of the nucleus to locate identical or nearly identical (homologous) sequences so that the broken end can pair up with this template and initiate local copying of this segment to patch up the chromosome break.  How this search takes place remains poorly understood.

The switching of budding yeast mating type genes has been a valuable model system in which to study the molecular events of broken chromosome repair, in real time.  It is possible to induce synchronously a site-specific double-strand break (DSB) on one chromosome, within the mating-type (MAT) locus.  At opposite ends of the same chromosome are two competing donor sequences with which the broken ends of the MAT sequence can pair up and copy new mating-type sequences into the MAT locus.

Normally one of these donors is used 9 times more often than the other.  We asked if this preference was irrevocable or if the bias could be changed by making the “wrong” donor more attractive – in this case by adding more sequences to that donor so that it shared more and more homology with the broken ends at MAT.  We found that the competition could indeed be changed and that adding more homologous sequences to the poorly-used donor increased its use.

In collaboration with Jané Kondev’s lab we devised both a “toy” model and a more rigorous thermodynamic model to explain these results.  They suggest that the Rad51 filament carrying the broken end of the MAT locus collides on average 4 times before with the preferred donor region before it actually succeeds in carrying out the next steps in the process that lead to repair and MAT switching.

Dynamics of homology searching during gene conversion in Saccharomyces cerevisiae revealed by donor competition Eric Coïc , Joshua Martin, Taehyun Ryu, Sue Yen Tay, Jané Kondev and James E. Haber. Genetics. 2011 Sep 27 2011 Sep 27

Three Leopards and a Shower

Dan Perlman passed along these notes from Briana Abrahms ’08, a Brandeis physics major whose focus has shifted to conservation issues and is in currently working in Botswana. Briana’s blog has more information, you can read it at http://www.conservationconnections.blogspot.com/

My Crash Course in Large Carnivores (Aug. 1, 2011)

Dear family and friends,

Greetings from Botswana! As many of you know, I’ve taken a six-month research position with the Botswana Predator Conservation Trust (BPCT) located outside the Moremi Game Reserve in northwestern Botswana. BPCT is a non-profit organization that works closely with the Botswana government to study and protect Botswana’s five large carnivores: lions, hyenas, African wild dogs, leopards, and cheetahs. (Read more at www.bpctrust.org!) A quick note about African wild dogs because its name can cause some confusion: African wild dogs are a distinct species (Lycaon pictus) just like the Gray wolf or the Spotted hyena, and do not refer to feral dog populations, as the name suggests. Because of habitat loss, disease, and competition with other carnivores, African wild dogs are one of the most endangered predators in Africa, with less than 1% of its former population remaining.

Within each of the five species that BPCT studies, several ‘representatives’ – usually one of the dominant animals in a pack – are radio collared and collect GPS data on their movements. So most of what we do on a day-to-day basis is drive around, see what animals we can pick up with our radio antennae, and then track them. We are the only organization who are permitted to go off road to look for animals, so we do a lot of exciting off-roading into the bush! Once we find the animal(s), we download the GPS data from its collar and make observations about what they are doing (eating, hunting, resting, caring for offspring, etc.) and what other animals it’s with at that time. The purpose of this is to collect data on the basic ecology and behavior of these species, for example: How much space does this species use? How does it share the landscape with other species? What does it eat? How do animals rise to dominance in a pack? The list goes on and on.

I got incredibly lucky on my first day here to witness a successful wild dog hunt that led to a steenbok kill (steenboks are like little antelope). Apparently this is really rare to see – the director of BPCT who’s been working here for over 20 years says he can count on one hand the number of times he’s seen a wild dog kill. And I saw it on my first day! Here’s a crudely edited video that I took with my camera, with footage of the camp I’m staying at, the wild dog hunt, and some of the other things I’ve seen. Be sure to check it out and notice the radio collars on some of the animals. Warning!: the video includes lions copulating and wild dogs killing and eating the steenbok, which can be a bit gruesome. (If the link doesn’t work for you, just search for ‘Botswana Day 1 – Wild Dog Hunt’ on YouTube).

A Tale of Three Leopards and a Shower (Oct. 15, 2011)

Hi all!

Here goes again with another monthly email. Last night I had what was probably my most exciting night at dog camp. Now that the dry season is in full swing here, we’ve been seeing more non-human visitors to our camp in search of water, which is generally found either in a bird bath near our kitchen area or our shower. Yesterday evening I came back from the field and met my coworkers Krys and Neil on their way out to find Chalak, a collared male leopard whose signal they had picked up very close to camp. We’d been very eager to find him because earlier this week he’d been seen mating with not one but TWO uncollared females within minutes of each other, which is very unusual because leopards are solitary and same-sexes generally don’t tolerate each other, at least from what BPCT researchers have seen.

Sure enough, about a half hour later I got a radio message from Krys saying they’d found Chalak and his two lady friends walking towards camp. It was dark by then, and I was alone in camp getting dinner ready in the kitchen. A few minutes later, I hadn’t heard anything more from Krys, but I did hear the loud snarling noise that one only hears when leopards are mating close by. It was obvious that they were somewhere in camp, though I couldn’t see them. The good thing was that I could localize where Chalak and one of the females were from the sounds of their mating, but I had no idea where the other female was.

As I stood in the kitchen near our radio, that question was solved as I saw one of the females emerge out of the bushes and head over to our bird bath, twenty feet away from where I was standing. Our kitchen (which is open, no walls) was the only structure around and there was nowhere safer for me to go, so I radioed Krys to let her know the situation and then I stayed put and kept an eye on the female. She didn’t seem interested in my presence. Then, just a few minutes later, I saw Chalak follow her out of the bushes and lay down by the bird bath. That really got my heart going – Chalak is a huge leopard, almost twice the size of the females, and I was standing twenty feet away from him with nothing in between. Again, though, his promiscuous evening had made him very thirsty and he was only interested in getting some water. After a few more minutes, the other female came, so now camp was occupied by three leopards and myself by my lonesome! I had quite the adrenaline rush. Not long after Krys and Neil finally came and pulled the truck right up to the kitchen. I climbed over a fridge in order to not exit the kitchen near the leopards and hopped into the truck. That was a huge relief. We tried to scare Chalak and the females off with the car to discourage them from using our camp as a drinking hole, but Chalak was so habituated to cars that he wasn’t bothered by it approaching him. Eventually he and the females made their way to the shower, where we heard some (probably hot and steamy) leopard mating roars. Krys and Neil ended up driving me to my tent and then parking the truck next to their tent so nobody had to walk around by themselves. This morning the leopards were out of camp but I saw one of them from my tent in the grassland behind camp, so they are still around. And thus the saga continues!

On another note, I decided to make a little “Day in the Life” video (shot very unprofessionally with my tiny digital camera) to hopefully give you a better sense of what I actually do here, how I spend my time, etc. I made this on October 7th, which turned out to be a pretty good day to choose for this project. Enjoy!


Complex Fluids Workshop on Sep 23

On Friday, Sep 23 2011, Brandeis will play host to the 48th New England Complex Fluids Meeting, run by the New England Complex Fluids Workgroup, of which the Brandeis Complex Fluids group is a charter participant. These quarterly meetings foster collaboration among researchers from industry and academia in the New England area studying Soft Condensed Matter, offer the opportunity to exchange ideas, and help introduce students and post-docs to the local academic and industrial research community.

The workshop, to be held in the Shapiro Campus Center, will have four talks by invited speakers, each about 30 minutes long with ample time for questions. In addition, everyone who attends is encouraged to give a five minute update (soundbite) of their current work.


9:30 AM – Krystyn Van Vliet (Materials Science and Engineering, MIT), Chemomechanics of responsive gels
10:15 AM – Jeremy England (Physics, MIT), Shape Shifting: the statistical physics of protein conformational change

Soundbites: 11:30 – 12:30 PM Five minute updates of current research

1:30 PM – Francis Starr (Physics, Wesleyan), DNA-linked Nanoparticle Assemblies
2:15 PM – Jennifer Ross (Physics, UMass Amherst), Controlling Microtubules Through Severing

More Soundbites: 3:30 PM – 4:30 PM

Geometry and Dynamics IGERT Awarded

Brandeis has just been awarded an NSF Integrative Graduate Education and Research Traineeship (IGERT) grant in the mathematical sciences.  The grant, titled Geometry and Dynamics: integrated education in the mathematical sciences, is designed to foster interdisciplinary research and education by and for graduate students across the mathematical and theoretical sciences, including chemistry, economics, mathematics, neuroscience, and physics.  It is structured around a number of themes common to these disciplines: complex dynamical systems, stochastic processes, quantum and statistical field theory; and geometry and topology. We believe that it is the first IGERT awarded for the theoretical (as opposed to laboratory) sciences, and are very excited about what we believe to be a highly novel program which will cement existing interdepartmental relationships and encourage exciting new collaborations in the mathematical sciences, including collaborations between the natural sciences and the International Business School (IBS).

The resolution of a singularity that develops along Ricci flow, understood mathematically by Grigori Perelman.  If the red manifold represents the target space of a string, it is conjectured that the corresponding two-dimensonal field theory describing the string undergoes confinement and develops a mass gap for the degrees of freedom corresponding to the singular regime.

The award, for $2,867,668 spread out over five years, provides funds for graduate student stipends, travel, seminar speakers, and interdisciplinary course development.  It contains activities and research opportunities in partnership with the New England Complex Systems Institute (NECSI) in Cambridge, MA.  It also provides opportunities for research internships at the International Center for the Theoretical Sciences in Bangalore.

The PIs on the grant are: Bulbul Chakraborty (Physics); Albion Lawrence (Physics: lead PI); Blake LeBaron (IBS); Paul Miller (Neuroscience); and Daniel Ruberman (Mathematics).  There are 11 additional affiliated Brandeis faculty across biology, chemistry, mathematics, neuroscience, physics, and psychology.  Contact Albion Lawrence (albion@brandeis.edu) for more information about the program.

Arrays of repulsively coupled Kuramoto oscillators on a triangular lattice organize into domains with opposite helicities in which phases of any three neighboring oscillators either increase or decrease in a given direction. Fig. (a) illustrates these two helicities in which cyan, ma- genta and blue vary in opposite directions. In Fig. (b), white and green regions represent domains of opposite helicities. The red regions indicate the frequency entrained oscillators, which are predominantly seen in the interior of the domains.

Admission to the program is handled through the Ph.D programs in the various disciplines:

Brandeis in Aspen II: Physics of granular materials

This post is a companion to Brandeis in Aspen I, and describes a workshop attended by Bulbul Chakraborty and Aparna Baskaran at the Aspen Center for Physics. The format of Aspen workshops is different from the usual academic workshop.  Each day has just one or two talks, which are primarily self-organized on a volunteer basis among the participants.  The format is designed to encourage  physicists working in a particular area to share research findings and enable cross-pollination of ideas in an informal and loosely structured setting.

The workshop attended by Chakraborty and Baskaran was entitled “Fluctuation and Response in granular materials”. Granular materials are ubiquitous in nature and industry. Examples range from sand and other geological materials, food and consumer products, and pebble beds in nuclear reactors. Understanding and controlling the properties of granular materials impacts such diverse processes as oil recovery, nuclear pebble bed reactors, printing and copying, and pharmaceutical processing. Granular media pose difficult and unique scientific challenges that distinguish them from atomic, nano-scale, and colloidal materials. Being intrinsically out of thermal equilibrium, assemblies of grains readily become trapped in metastable states, are extremely sensitive to preparation conditions, and can have strongly time-dependent properties.  Relaxing the constraints of thermal equilibrium, however, offers an advantage by opening up possibilities for creating novel static and dynamic phases that have distinctive functional properties.

At Aspen, the one-on-one and small sub group interactions among the participants covered a wide range of topics that are at the forefront of materials research, however, the program as a whole primarily focused on two questions. The first question was: What do we understand about jamming of granular materials? Jamming is what occurs in everyday life when we are trying to get coffee beans out of a hopper and they suddenly stop flowing. We fix this by tapping on the hopper. But this same phenomenon when it happens in giant grain silos causes them to collapse. So, one of the challenges is to be able to predict jamming events. The role of the physicist here is to design and carry out experiments in minimal model systems and develop theoretical frameworks that lead to predictive models of observed phenomena. Statistical Mechanics provides a powerful theoretical tool to address this question and our own Professor Chakraborty is one of the leading experts in the theory of jamming. The participants at the workshop had several robust discussions on the current understanding of this phenomenon and theoretical and experimental challenges that remain to be addressed.

The second question that the workshop focused on was : How does a dense granular material behave when sheared? Granular materials are called rheological fluids in that they exhibit shear-thinning and shear thickening behavior. In everyday life, we are all familiar with shear thinning. When we squeeze a tube of toothpaste, we are shearing it and it flows onto our brush. But once on the brush it stays put. This behavior is called shear thinning. Understanding rheology of granular materials is important for diverse applications ranging from pharmaceutical processes to being able to print well. The participants discussed in detail the physics of sheared granular materials and shared insight obtained from theory, simulations and experiments.

All participants departed the workshop invigorated by the robust exchange of ideas, ready to address the challenges presented by these complex materials.

Brandeis in Aspen I: String theory and quantum information

The Aspen Center for Physics is a physics retreat in which groups of researchers in a given field gather for a few weeks during the summer to discuss the latest developments and create the next ones. This May, a record four Brandeis physicists — almost a quarter of the department — visited the Center at the same time, attending two different workshops. This posting is about a workshop attended by string theorists Matthew Headrick and Albion Lawrence (and co-organized by Headrick);  another posting will describe a workshop attended by condensed-matter theorists Aparna Baskaran and Bulbul Chakraborty (a member of the Center’s advisory board).  Entry into Aspen workshops is competitive, so this strong Brandeis representation is remarkable; as always, we punch above our weight.

Headrick and Lawrence attended the workshop Quantum information in quantum gravity and condensed matter physics.  This was a highly interdisciplinary workshop, which brought together specialists in quantum gravity, including Headrick and Lawrence; experts in quantum information theory; and experts in “hard” condensed matter physics (who study material properties for which quantum phenomena play a central role).

Quantum information theorists study how the counterintuitive features of quantum mechanics — such as superpositions of states, entanglement between separated systems, and the collapse of the wave function brought on by measurement — could be exploited to produce remarkable (but so far mostly hypothetical) technologies like teleportation of quantum states, unbreakable encryption, and superfast computation. What does this have to do with gravity? When we try to formulate a consistent quantum-mechanical theory of gravity — which would subsume Einstein’s classical general theory of relativity — the concept of information crops up in numerous and often puzzling ways. For example, Stephen Hawking showed in the 1970s that, on account of quantum effects, black holes emit thermal radiation. Unlike the radiation emitted by conventional hot objects, which is only approximately thermal, pure thermal radiation of the kind that Hawking’s calculation predicted cannot carry information. Many physicists (including Hawking) therefore originally interpreted his result as implying that black holes fundamentally destroy information, challenging a sacred principle of physics. Today, based on advances in string theory, physicists (including Hawking) generally believe that in fact black holes do not destroy the information they contain.  Rather, black holes hide information in very subtle ways, by scrambling, encryption, and perhaps quantum teleportation — in other words, the same kinds of tricks that the quantum information people have been inventing and studying independently at the same time.

Another connection between gravity and information is provided by the so-called “holographic principle”, which also arose in the study of black holes and which has been given a precise realization in the context of string theory. This principle posits that, due to a combination of gravitational and quantum effects, there is a fundamental limit to the amount of information (i.e. the number of bits) that can be stored in a region of space, and furthermore that limit is related to its surface area, not its volume. String theorists, beginning with the seminal work of Juan Maldacena, have uncovered a number of precise implementations of this principle, in which certain quantum theories without gravity are holograms of theories of quantum gravity.  This should provide an avenue for uncovering the “tricks” gravity uses to hide information, a subject Lawrence is active in.  An additional benefit of these implementations is that calculations in the nongravitational theories which seemed prohibitively difficult become fairly simple in the gravitational side; these include  the computation of interesting quantities in quantum information theory, an area in which Headrick has done influential work.

All of these issues and many others were discussed in Aspen. This rather unique workshop was a very fruitful exchange of ideas, with physicists from three fields learning from each other and forging new interdisciplinary collaborations, in a setting where the scenery matched the grandeur of the subject.

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