Pump without pumps

14 04 2017

By Kun-Ta Wu, Ph.D.

Pumping water through a pipe solves the need to provide water in every house. By turning on faucets, we retrieve water at home without needing to carry it from a reservoir with buckets. However, driving water through a pipe requires external pressure; such pressure increases linearly with pipe length. Longer pipes need to be more rigid for sustaining proportionally-increased pressure, preventing pipes from exploding. Hence, transporting fluids through pipes has been a challenging problem for physics as well as engineering communities.

To overcome such a problem, Postdoctoral Associate Kun-Ta Wu and colleagues from the Dogic and Fraden labs, and Brandeis MRSEC doped water with 0.1% v/v active matter. The active matter mainly consisted of kinesin-driven microtubules. These microtubules were extracted from cow brain tissues. In cells, microtubules play an important role in cell activity, such as cell division and nutrient transport. The activity originates from kinesin molecular motors walking along microtubules. In cargo transport, microtubules are like rail tracks; kinesin motors are like trains. When these tracks and trains are doped in water, their motion drives surrounding fluids, generating vortices. The vortices only circulate locally; there is no global net flow.

Wu-Pump without Pumps

Figure: Increasing the height of the annulus induces a transition from locally turbulent to globally coherent flows of a confined active isotropic fluid. The left and right half-plane of each annulus illustrate the instantaneous and time-averaged flow and vorticity map of the self-organized flows. The transition to coherent flows is an intrinsically 3D phenomenon that is controlled by the aspect ratio of the channel cross section and vanishes for channels that are either too shallow or too thin. Adapted from Wu et al. Science 355, eaal1979 (2017).

To create a net flow like rivers, Wu et al. discovered that confining such an active fluid in a toroid triggers a transition from turbulent to coherent flowing states (Figure, above left). Unlike rivers, which gain kinetic energy from their gravitational potential, such a fluid is driven by kinesin motors consuming internal chemical energy (adenosine triphosphate), self-pumping without external pressure. However, not all toroidal geometries sustain coherent flows. Wu et al. pointed out that sustaining coherent flows requires the toroidal cross section to have a shape similar to a square or circle. In a thin and wide toroid, the coherent flow is suppressed (Figure, above right). Wu et al. demonstrated that with a proper (circular) cross section, the coherent flow can persist for meters, proving the feasibility of transporting fluids at a macroscopic scale without external pressure.

In conclusion, Wu et al. invented self-pumping fluids. The fluids flow in a pipe without external pressure. However, the knowledge of self-pumping fluids remains limited. For example, why does the transition from turbulent to coherent flow depend on the shape of the pipe cross section, rather than its absolute size? How does the coherent flow respond to external pressure? Answering these questions are the key to understanding underlying principles of self-organization of active fluids; however, Wu et al.’s invention already opens the door to pumping fluids without a pump.

Kun-Ta Wu, Jean Bernard Hishamunda, Daniel T.N. Chen, Stephen J. DeCamp, Ya-Wen Chang, Alberto Fernández-Nieves, Seth Fraden, and Zvonimir Dogic. Transition from turbulent to coherent flows in confined three-dimensional active fluids. Science 355, eaal1979 (2017). doi:10.1126/science.aal1979.



Physics Graduate Student Receives Kavli Fellowship

12 04 2017

Cesar Agon at Kavli Institute Cesar Agon, a graduate student in the High-Energy and Gravitational Theory group, was awarded a prestigious Graduate Fellowship at the Kavli Institute for Theoretical Physics (KITP) at the University of California, Santa Barbara. KITP is one of the world’s leading centers for research in all areas of theoretical physics. In addition to having its own faculty and postdocs, it hosts visiting faculty from around the world and holds conferences and semester-long programs on topics of current interest. The Graduate Fellowship program allows exceptional students to benefit from this activity and the scientific ambience of KITP by spending a semester there. This is a very competitive program, with only about half a dozen students coming from around the world each semester. Agon, who is advised by Profs. Matthew Headrick, Albion Lawrence, and Howard Schnitzer, is currently spending the spring term at KITP, before heading off to Stony Brook University as a postdoc in the fall.

Back in the summer of 2015, Agon had the opportunity to visit KITP during two important programs on the physics frontiers, both of special interest to him, namely ”Entanglement in Strongly-Correlated Quantum Matter” and ”Quantum Gravity Foundations: UV to IR”. That was a great opportunity to meet in person the leaders of the field from around the world in the relaxed and friendly atmosphere of the KITP. Discussions among the researchers and students were tremendously common all around the institute and there were many activities that facilitated such discussions such as daily coffees, lunches, and dinners.

In his new visit as a Graduate Fellow in 2017, Agon has found once again most of what he saw in his previous visit. The current program, “Scattering Amplitudes and Beyond”, expands his current knowledge of Quantum Field Theory and is of help in his preparation for his upcoming postdoctoral job. Scattering amplitudes are quantities of interest in quantum field theory since they encode the basic information one needs to make predictions and test them against accelerator experiments. In addition, being a local now allows him to explore more of what KITP and UCSB have to offer. Faculty, postdocs, and grad students discuss physics every day over lunch overlooking the beautiful lagoon. Furthermore, two seminars are programmed weekly, as well as colloquia and postdoc and graduate student journal clubs. These kinds of activities are extremely useful, as they facilitate the essential but difficult process of being up to date on the relevant current work in the field (broadly defined), and making collaborations with various members of both KITP and UCSB easier and more natural for him.

During his stay, Agon has had the opportunity to give talks at local events (Pacific Gravity Meeting) as well as at the weekly group seminar, and he has started a collaboration with KITP postdoc Tomonori Ugajin on some interesting entanglement entropy related projects. One of them seeks to study the gravitational duals to certain contributions to the entanglement entropy of excited CFT states, while the second looks for a better understanding of the universal behavior of the ground state entanglement entropy between disjoint regions in the small separation regime. His preliminary work has been dedicated to studying some of the techniques that have proved useful in previous work (related to bulk emergence and the proofs of energy conditions on quantum field theories) and which they believe will be also useful in solving these problems.

Although the scientific activity was Agon’s main motivation to visit KITP, one has to also acknowledge the beauty that Santa Barbara and its surroundings offer. The most remarkable for him was the enormous diversity of the natural environment, which is not limited to the gorgeous beaches but also includes a variety of fauna and flora in the nearby mountains, which range from the tropical to dessert-like, and the vast flat lands that fill the space in between, all of this in an almost invariant perfect weather all year long. The city itself keeps a beautiful Spanish Colonial architecture, an authentic and large variety of delicious Mexican cuisine, and a considerable amount of cultural activities with special emphasis on art in all its forms.



Physics Graduate Student Receives Kavli Fellowship

12 04 2017

Cesar Agon at Kavli Institute Cesar Agon, a graduate student in the High-Energy and Gravitational Theory group, was awarded a prestigious Graduate Fellowship at the Kavli Institute for Theoretical Physics (KITP) at the University of California, Santa Barbara. KITP is one of the world’s leading centers for research in all areas of theoretical physics. In addition to having its own faculty and postdocs, it hosts visiting faculty from around the world and holds conferences and semester-long programs on topics of current interest. The Graduate Fellowship program allows exceptional students to benefit from this activity and the scientific ambience of KITP by spending a semester there. This is a very competitive program, with only about half a dozen students coming from around the world each semester. Agon, who is advised by Profs. Matthew Headrick, Albion Lawrence, and Howard Schnitzer, is currently spending the spring term at KITP, before heading off to Stony Brook University as a postdoc in the fall.

Back in the summer of 2015, Agon had the opportunity to visit KITP during two important programs on the physics frontiers, both of special interest to him, namely ”Entanglement in Strongly-Correlated Quantum Matter” and ”Quantum Gravity Foundations: UV to IR”. That was a great opportunity to meet in person the leaders of the field from around the world in the relaxed and friendly atmosphere of the KITP. Discussions among the researchers and students were tremendously common all around the institute and there were many activities that facilitated such discussions such as daily coffees, lunches, and dinners.

In his new visit as a Graduate Fellow in 2017, Agon has found once again most of what he saw in his previous visit. The current program, “Scattering Amplitudes and Beyond”, expands his current knowledge of Quantum Field Theory and is of help in his preparation for his upcoming postdoctoral job. Scattering amplitudes are quantities of interest in quantum field theory since they encode the basic information one needs to make predictions and test them against accelerator experiments. In addition, being a local now allows him to explore more of what KITP and UCSB have to offer. Faculty, postdocs, and grad students discuss physics every day over lunch overlooking the beautiful lagoon. Furthermore, two seminars are programmed weekly, as well as colloquia and postdoc and graduate student journal clubs. These kinds of activities are extremely useful, as they facilitate the essential but difficult process of being up to date on the relevant current work in the field (broadly defined), and making collaborations with various members of both KITP and UCSB easier and more natural for him.

During his stay, Agon has had the opportunity to give talks at local events (Pacific Gravity Meeting) as well as at the weekly group seminar, and he has started a collaboration with KITP postdoc Tomonori Ugajin on some interesting entanglement entropy related projects. One of them seeks to study the gravitational duals to certain contributions to the entanglement entropy of excited CFT states, while the second looks for a better understanding of the universal behavior of the ground state entanglement entropy between disjoint regions in the small separation regime. His preliminary work has been dedicated to studying some of the techniques that have proved useful in previous work (related to bulk emergence and the proofs of energy conditions on quantum field theories) and which they believe will be also useful in solving these problems.

Although the scientific activity was Agon’s main motivation to visit KITP, one has to also acknowledge the beauty that Santa Barbara and its surroundings offer. The most remarkable for him was the enormous diversity of the natural environment, which is not limited to the gorgeous beaches but also includes a variety of fauna and flora in the nearby mountains, which range from the tropical to dessert-like, and the vast flat lands that fill the space in between, all of this in an almost invariant perfect weather all year long. The city itself keeps a beautiful Spanish Colonial architecture, an authentic and large variety of delicious Mexican cuisine, and a considerable amount of cultural activities with special emphasis on art in all its forms.



Two Brandeis Professors Receive 2017 Simons Fellowships

11 04 2017
Bit threads in a holographic spacetime

Bit threads in a holographic spacetime

Two Brandeis professors have been awarded Simons Fellowships for 2017. Daniel Ruberman received the 2017 Simons Fellows in Mathematics. Matthew Headrick was awarded the 2017 Simons Fellows in Theoretical Physics. This is the first of two articles where each recipient’s award-winning research is described.

Matthew Headrick’s research studies the phenomenon of entanglement in certain quantum systems and its connection to the geometry of spacetime in general relativity. This very active area of research is the culmination of three developments in theoretical physics over the past 20 years.

First, in 1997, string theorists discovered that certain quantum systems involving a large number of very strongly interacting constituents — whose analysis would normally be intractable — are secretly equivalent to general relativity — a classical theory describing gravity in terms of curved spacetime — in a space with an extra dimension. For example, if the quantum system has two dimensions of space, then the general relativity has three; the phenomenon is thus naturally dubbed “holography”.

This equivalence between two very different-looking theories is incredibly powerful, and has led to much progress in understanding both strongly-interacting quantum systems and general relativity. However, it is still not fully understood how or precisely under what conditions such an equivalence holds.

Meanwhile, around 15 years ago, theorists began studying entanglement as a way to understand the behavior of quantum systems. “Entanglement” refers to correlations between two parts of a quantum system that occurs at the level of the wave function (unlike more familiar classical, or statistical, correlations). Entanglement is responsible for much of the apparent weirdness of quantum mechanics, as well as the power of such potential technologies as quantum cryptography and quantum computers. Although the concept of entanglement has been recognized almost since the birth of quantum mechanics, only recently has it been understood how quantifying entanglement (using certain kinds of entropies) provides powerful insights into the behavior of quantum systems ranging from many-body condensed-matter systems to theories of particle physics.

These two developments came together in 2006, when two physicists, Ryu and Takayanagi — one a condensed-matter theorist and the other a string theorist — made a dramatic conjecture connecting them. They posited that, in a holographic system, the entanglement is directly related to the geometry of space on the general relativity side; more specifically, given a decomposition of the quantum system into two parts, the amount of entanglement is given by the area of a certain minimal surface on the general relativity side. This development has led to many advances in our understanding of entanglement in strongly-interacting systems, and has provided a new framework for thinking about the emergence of space out of quantum constituents.

Since the Ryu-Takayanagi conjecture was originally made, Headrick has been a leader in testing, generalizing, and applying it. Working with Michael Freedman (Microsoft Research), he recently discovered a new way to understand entanglement in holographic systems in terms of microscopic “bit threads” running through space; using the so-called max flow-min cut theorem from network theory, they showed that this picture precisly reproduces the predictions of the Ryu-Takayanagi formula. With his students and other collaborators, Headrick is currently building on this picture. A major focus, for example, is to understand the subtle role that time plays in entanglement and holography.



“Exceptionally Helpful” Matthew Headrick Receives Award

9 03 2017

Associate Professor of Physics Matthew Headrick was named by the American Physical Society as an Outstanding Referee for 2017. The award recognizes “scientists who have been exceptionally helpful in assessing manuscripts for publication in the APS journals”. Headrick, who works in string theory and related areas of theoretical physics, is one of 150 Outstanding Referees named this year, out of about 60,000 active referees for the APS journals. Headrick is not the only Brandeis physicist to receive this honor; Robert Meyer, now Emeritus Professor, was named an Outstanding Referee in 2011.

Headrick’s research is primarily focused on the intersection of quantum gravity, quantum field theory, and quantum information theory. He is specifically interested in information-theoretic aspects of holographic field theories (field theories that are dual to higher-dimensional gravitational theories), such as entanglement entropies and related quantities.



Research Funding For Undergrads: MRSEC Summer Materials Undergraduate Research Fellowships

30 01 2017

The Division of Science wishes to announce that, in 2017, we will offer seven MRSEC Summer  Materials Undergraduate Research Fellowships (SMURF) for Brandeis students doing undergraduate research, sponsored by the Brandeis Materials Research Science and Engineering Center.

The fellowship winners will receive $5,000 stipends (housing support is not included) to engage in an intensive and rewarding research and development program that consists of full-time research in a MRSEC lab, weekly activities (~1-2 hours/week) organized by the MRSEC Director of Education, and participation in SciFest VII on Aug 3, 2017.

The due date for applications is February 27, 2017, at 6:00 PM EST.

To apply, the application form is online and part of the Unified Application: https://goo.gl/9LcSpG (Brandeis login required).


Eligibility

Students are eligible if they will be rising Brandeis sophomores, juniors, or seniors in Summer 2017 (classes of ’18, ’19, and ’20). No prior lab experience is required. A commitment from a Brandeis MRSEC member to serve as your mentor in Summer 2017 is required though. The MRSEC faculty list is: http://www.brandeis.edu/mrsec/people/index.html

Conflicting Commitments
SMURF recipients are expected to be available to do full time laboratory research between May 30 – August 4, 2017. During that period, SMURF students are not allowed to take summer courses, work another job or participate in extensive volunteer/shadowing experiences in which they commit to being out of the lab for a significant amount of time during the summer. Additionally, students should not be paid for doing lab research during this period from other funding sources.

Application Resources
Interested students should apply online (Brandeis login required). Questions that are not answered in the online FAQ may be addressed to Steven Karel <divsci at brandeis.edu>.



Division of Science Hosts the 2016 Undergraduate Science Symposium

21 09 2016

Written by Jena Pitman-Leung.

uss-img1

The Division of Science Graduate Affairs group hosted the 2nd annual Brandeis University Undergraduate Science Symposium on Saturday 17th, 2016. More than 60 students representing institutions from Massachusetts, Rhode Island, and New Hampshire attended the event, which was held in the Shapiro Science Center. The morning session included research talks from faculty in the Life Sciences (Don Katz, Liz Hedstrom) and the Physical Sciences (Matt Headrick, Christine Thomas), followed by panel discussions with faculty in the Life Sciences (Liz Hedstrom, Bruce Goode, and Maria Miara) and Physical Sciences (Gabriella Sciolla, Isaac Krauss, Jordan Pollack) on how to apply to graduate school. The students then came together for a networking lunch with Brandeis students, postdocs, and faculty. Lunch was followed by a well attended poster session, where 38 students had the opportunity to present their independent research. The day ended by awarding prizes for the best posters in five disciplines. The winners were:

Biology: Rahim Hirani, Hampshire College, “The regulatory role of Beta-Arrestin 1 in prostate cancer cell proliferation”
Neuroscience: Paige Miranda, Wellesley College, “Metabolic Processes Driving Hippocampal Long Term Potentiatio”
Biochemistry: Myfanwy Adams, Wellesley College, “Expression of a Cardiac ATP-sensitive Potassium Channel in a Heterologous Cell Line”
Chemistry: Natsuko Yamagata, Brandeis University, “Exploring the Unexplored: Supramolecular Hydrogels of Retro-Inverso Peptides for 3D Cell Culture”
Physics: Jameson O’Reilly, Northeastern University, “A capillary-mimicking optical tissue phantom for diffuse correlation spectroscopy”

The Division of Science is committed to supporting local undergraduate research, and is excited about the possibility of these bright young scientist choosing Brandeis for their graduate study. We look forward to hosting similar events in the future!



SciFest VI recap and stats

11 08 2016

The Brandeis University Division of Science held its annual undergraduate research poster session SciFest VI on August 4, 2016, as a record number of student researchers presented posters with the results of their summer’s (or last year’s) worth of independent research. We had a great audience of grad students, postdocs, faculty, proud parents, and senior administrators.

More pictures and abstract books are available at the SciFest site.

SciFest VI by numbers






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