“Iris is great - she was on a researcher on my Gen Y book when she was still in her teens and has been a researcher on my freelance articles. Highly recommended!”
About
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After years of dedicated research, an incredible milestone has been achieved in the field of gene therapies. Sarepta Therapeutics recently received…
After years of dedicated research, an incredible milestone has been achieved in the field of gene therapies. Sarepta Therapeutics recently received…
Liked by Iris Stone, PhD
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I'm thrilled to announce that the Straehla Lab is relocating to Seattle this fall! I will be a Principal Investigator in the Ben Towne Center at…
I'm thrilled to announce that the Straehla Lab is relocating to Seattle this fall! I will be a Principal Investigator in the Ben Towne Center at…
Liked by Iris Stone, PhD
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We're hiring! Check out our open positions and be a part of an innovative team studying how brain circuitry and activity drive behavior, learning…
We're hiring! Check out our open positions and be a part of an innovative team studying how brain circuitry and activity drive behavior, learning…
Liked by Iris Stone, PhD
Experience & Education
Publications
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Spectral learning of Bernoulli linear dynamical systems models
Transactions on Machine Learning Research
Latent linear dynamical systems with Bernoulli observations provide a powerful modeling framework for identifying the temporal dynamics underlying binary time series data, which arise in a variety of contexts such as binary decision-making and discrete stochastic processes such as binned neural spike trains. Here, we develop a spectral learning method for fast, efficient fitting of Bernoulli latent linear dynamical system (LDS) models. Our approach extends traditional subspace identification…
Latent linear dynamical systems with Bernoulli observations provide a powerful modeling framework for identifying the temporal dynamics underlying binary time series data, which arise in a variety of contexts such as binary decision-making and discrete stochastic processes such as binned neural spike trains. Here, we develop a spectral learning method for fast, efficient fitting of Bernoulli latent linear dynamical system (LDS) models. Our approach extends traditional subspace identification methods to the Bernoulli setting via a transformation of the first and second sample moments. This results in a robust, fixed-cost estimator that avoids the hazards of local optima and the long computation time of iterative fitting procedures like the expectation-maximization (EM) algorithm. In regimes where data is limited or assumptions about the statistical structure of the data are not met, we demonstrate that the spectral estimate provides a good initialization for Laplace-EM fitting. Finally, we show that the estimator provides substantial benefits to real world settings by analyzing data from mice performing a sensory decision-making task.
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Charge Transport through Superexchange in Phenothiazine–7, 7, 8, 8-Tetracyanoquinodimethane (PTZ–TCNQ) Cocrystal Microribbon FETs Grown Using Evaporative Alignment.
ACS Applied Electronic Materials
Charge transfer (CT) cocrystals, molecular crystals composed of electron donating and accepting species, are being developed for applications in optoelectronics. Here we present optical and electronic characterization of the CT cocrystal phenothiazine–tetracyanoquinodimethane (PTZ–TCNQ). This material has a broad NIR absorption peak with an optical band edge less than 0.6 eV. We used density functional theory calculations to identify the origin of the low energy CT states and changes in the…
Charge transfer (CT) cocrystals, molecular crystals composed of electron donating and accepting species, are being developed for applications in optoelectronics. Here we present optical and electronic characterization of the CT cocrystal phenothiazine–tetracyanoquinodimethane (PTZ–TCNQ). This material has a broad NIR absorption peak with an optical band edge less than 0.6 eV. We used density functional theory calculations to identify the origin of the low energy CT states and changes in the Raman spectra. We also demonstrate the fabrication of long, ribbon-like oriented cocrystals using an evaporative alignment method. Cocrystals grown on Si substrates were fabricated into organic field effect transistors. Despite theoretical predictions of ambipolarity, only electron conduction was observed, with mobilities on the order of 10–4 cm2 V–1 s–1. Measurements of the temperature dependence of the mobility indicated a superexchange mediated hopping mechanism for charge transport, with a characteristic energy scale of 0.19 eV.
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Opponent control of behavior by dorsomedial striatal pathways depends on task demands and internal state
Nature Neuroscience
A classic view of the striatum holds that activity in direct and indirect pathways oppositely modulates motor output. Whether this involves direct control of movement, or reflects a cognitive process underlying movement, has remained unresolved. Here we find that strong, opponent control of behavior by the two pathways of the dorsomedial striatum (DMS) depends on a task9s cognitive demands. Furthermore, a latent state model (a hidden markov model with generalized linear model observations)…
A classic view of the striatum holds that activity in direct and indirect pathways oppositely modulates motor output. Whether this involves direct control of movement, or reflects a cognitive process underlying movement, has remained unresolved. Here we find that strong, opponent control of behavior by the two pathways of the dorsomedial striatum (DMS) depends on a task9s cognitive demands. Furthermore, a latent state model (a hidden markov model with generalized linear model observations) reveals that - even within a single task - the contribution of the two pathways to behavior is state-dependent. Specifically, the two pathways have large contributions in one of two states associated with a strategy of evidence accumulation, compared to a state associated with a strategy of repeating previous choices. Thus, both the cognitive demands imposed by a task, as well as the strategy that mice pursue within a task, determine whether DMS pathways provide strong and opponent control of behavior.
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Mice alternate between discrete strategies during perceptual decision-making
Nature Neuroscience
Classical models of perceptual decision-making assume that animals use a single, consistent strategy to form decisions, or that decision-making strategies evolve slowly over time. Here we present new analyses suggesting that this common view is incorrect. We analyzed data from two mouse decision-making experiments and found that choice behavior relies on an interplay between multiple interleaved strategies. These strategies, characterized by states in a hidden Markov model, persist for tens to…
Classical models of perceptual decision-making assume that animals use a single, consistent strategy to form decisions, or that decision-making strategies evolve slowly over time. Here we present new analyses suggesting that this common view is incorrect. We analyzed data from two mouse decision-making experiments and found that choice behavior relies on an interplay between multiple interleaved strategies. These strategies, characterized by states in a hidden Markov model, persist for tens to hundreds of trials before switching, and may alternate multiple times within a session. The identified strategies were highly consistent across animals, consisting of a single "engaged" state, in which decisions relied heavily on the sensory stimulus, and several biased or disengaged states in which errors frequently occurred. These results provide a powerful alternate explanation for "lapses" often observed in psychophysical experiments, and suggest that standard measures of performance mask the presence of dramatic changes in strategy across trials.
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The structural phases and vibrational properties of Mo1-xWxTe2 alloys.
2D Materials
The structural polymorphism in transition metal dichalcogenides (TMDs) provides exciting opportunities for developing advanced electronics. For example, MoTe2 crystallizes in the 2H semiconducting phase at ambient temperature and pressure, but transitions into the 1T' semimetallic phase at high temperatures. Alloying MoTe2 with WTe2 reduces the energy barrier between these two phases, while also allowing access to the T d Weyl semimetal phase. The $\text{M}{{\text{o}}_{1-\text{x}}}$ WxTe2 alloy…
The structural polymorphism in transition metal dichalcogenides (TMDs) provides exciting opportunities for developing advanced electronics. For example, MoTe2 crystallizes in the 2H semiconducting phase at ambient temperature and pressure, but transitions into the 1T' semimetallic phase at high temperatures. Alloying MoTe2 with WTe2 reduces the energy barrier between these two phases, while also allowing access to the T d Weyl semimetal phase. The $\text{M}{{\text{o}}_{1-\text{x}}}$ WxTe2 alloy system is therefore promising for developing phase change memory technology. However, achieving this goal necessitates a detailed understanding of the phase composition in the MoTe2-WTe2 system. We combine polarization-resolved Raman spectroscopy with x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) to study bulk $\text{M}{{\text{o}}_{1-\text{x}}}$ WxTe2 alloys over the full compositional range x from 0 to 1. We identify Raman and XRD signatures characteristic of the 2H, 1T', and T d structural phases that agree with density-functional theory (DFT) calculations, and use them to identify phase fields in the MoTe2–WTe2 system, including single-phase 2H, 1T', and T d regions, as well as a two-phase 1T' + T d region. Disorder arising from compositional fluctuations in $\text{M}{{\text{o}}_{1-\text{x}}}$ WxTe2 alloys breaks inversion and translational symmetry, leading to the activation of an infrared 1T'-MoTe2 mode and the enhancement of a double-resonance Raman process in $\text{2H-M}{{\text{o}}_{1-\text{x}}}$ WxTe2 alloys. Compositional fluctuations limit the phonon correlation length, which we estimate by fitting the observed asymmetric Raman lineshapes with a phonon confinement model. These observations reveal the important role of disorder in $\text{M}{{\text{o}}_{1-\text{x}}}$ WxTe2 alloys, clarify the structural phase boundaries, and provide a foundation for future explorations of phase transitions and electronic phenomena in this system.
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Phonon anharmonicity in bulk Td-MoTe2
Applied Physics Letters
We examine anharmonic contributions to the optical phonon modes in bulk Td-MoTe2 through temperature-dependent Raman spectroscopy. At temperatures ranging from 100 K to 200 K, we find that all modes redshift linearly with temperature in agreement with the Grüneisen model. However, below 100 K, we observe nonlinear temperature-dependent frequency shifts in some modes. We demonstrate that this anharmonic behavior is consistent with the decay of an optical phonon into multiple acoustic phonons…
We examine anharmonic contributions to the optical phonon modes in bulk Td-MoTe2 through temperature-dependent Raman spectroscopy. At temperatures ranging from 100 K to 200 K, we find that all modes redshift linearly with temperature in agreement with the Grüneisen model. However, below 100 K, we observe nonlinear temperature-dependent frequency shifts in some modes. We demonstrate that this anharmonic behavior is consistent with the decay of an optical phonon into multiple acoustic phonons. Furthermore, the highest frequency Raman modes show large changes in intensity and linewidth near T ≈ 250 K that correlate well with the Td→1T′ structural phase transition. These results suggest that phonon-phonon interactions can dominate anharmonic contributions at low temperatures in bulk Td-MoTe2, an experimental regime that is currently receiving attention in efforts to understand Weyl semimetals.
Courses
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Brains, Minds, and Machines (BMM) Summer Course at the Marine Biology Laboratory
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Summer Workshop on the Dynamic Brain (SWDB) at Friday Harbor Laboratory
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Honors & Awards
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F31 National Research Service Award (NRSA)
National Institutes of Health (NIH)
The purpose of the Ruth L. Kirschstein National Research Service Award (NRSA) Individual Predoctoral Fellowship (Parent F31) award is to enable promising predoctoral students to obtain individualized, mentored research training from outstanding faculty sponsors while conducting dissertation research in scientific health-related fields relevant to the missions of the participating NIH Institutes and Centers. The proposed mentored research training must reflect the candidate’s dissertation…
The purpose of the Ruth L. Kirschstein National Research Service Award (NRSA) Individual Predoctoral Fellowship (Parent F31) award is to enable promising predoctoral students to obtain individualized, mentored research training from outstanding faculty sponsors while conducting dissertation research in scientific health-related fields relevant to the missions of the participating NIH Institutes and Centers. The proposed mentored research training must reflect the candidate’s dissertation research project and is expected to clearly enhance the individual’s potential to develop into a productive, independent research scientist. It is amongst the most prestigious fellowships available to graduate students in health science fields in the United States.
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COSYNE Travel Grant
Computational and Systems Neuroscience (COSYNE) Conference Grant Program
Monetary award assists with conference travel and is granted to early-career scientists with highly scored abstracts who are traveling to present their work at the COSYNE annual meeting. Selection is determined primarily based on merit (reviewer scores).
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G. Wallace Ruckert ’30 Fellowship Fund Recipient
Princeton University Graduate School
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Outstanding Graduating Senior
George Mason University Department of Physics and Astronomy
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NSF Graduate Research Fellowship Program - Honorable Mention
National Science Foundation
The NSF Graduate Research Fellowship Program recognizes and supports outstanding graduate students in NSF-supported science, technology, engineering, and mathematics disciplines who are pursuing research-based Master's and doctoral degrees at accredited United States institutions.
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Outstanding Rising Senior
George Mason University Department of Physics and Astronomy
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Goldwater Scholarship
The Barry Goldwater Scholarship and Excellence in Education Foundation
https://goldwater.scholarsapply.org/2017-scholars/
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OSCAR Fellow
Office of Student Scholarship, Creative Activities, and Research
http://oscar.gmu.edu/students/oscar-fellows.cfm
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Intenstive Undergraduate Research Scholars Program (URSP) Grant
Office of Student Scholarship, Creative Activities, and Research
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OSCAR Student Excellence Award
Office of Student Scholarship, Creative Activities, and Research
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Outstanding Undergraduate Research Award
George Mason University Physics Department
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Schwartzstein Honors College Summer Research Award
George Mason University Honors College
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Ken Haas Outstanding Student Paper Award (Runner Up)
American Physical Society Forum on Industrial and Applied Physics
https://www.aps.org/units/fiap/awards/hass.cfm
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Traditional Undergraduate Research Scholars Program (URSP) Grant
Office of Student Scholarship, Creative Activities, and Research
Languages
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Spanish
Professional working proficiency
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English
Native or bilingual proficiency
Organizations
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Sigma Xi
Associate Member
- PresentSigma Xi, The Scientific Research Honor Society is the international honor society of science and engineering. One of the oldest and largest scientific organizations in the world, Sigma Xi has a distinguished history of service to science and society for more than one hundred and twenty five years. Scientists and engineers, whose research spans the disciplines of science and technology, comprise the membership of the Society. Sigma Xi chapters can be found at colleges and universities…
Sigma Xi, The Scientific Research Honor Society is the international honor society of science and engineering. One of the oldest and largest scientific organizations in the world, Sigma Xi has a distinguished history of service to science and society for more than one hundred and twenty five years. Scientists and engineers, whose research spans the disciplines of science and technology, comprise the membership of the Society. Sigma Xi chapters can be found at colleges and universities, government laboratories, and industry research centers around the world. More than 200 Nobel Prize winners have been members.
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Phi Kappa Phi National Honors Society
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- PresentThe oldest all-discipline honors society in the United States. Membership is by invitation only and is restricted to students with integrity and high ethical standards and who are ranked scholastically in the top 7.5 percent (second-semester juniors) and the top 10 percent (seniors and graduate students) of their class.
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Amazing Python library: PyOD. Use it to detect anomalies in multivariate data. Works whether you’re tackling a small-scale project or large…
Amazing Python library: PyOD. Use it to detect anomalies in multivariate data. Works whether you’re tackling a small-scale project or large…
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