Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
2,921
result(s) for
"Brown, Adam"
Sort by:
A quantum complexity lower bound from differential geometry
Differential geometry has long found applications in physics in general relativity and related areas. More recently, it was proposed by Nielsen that the tools of differential geometry, when applied to the unitary group, might be used to bound the complexity of quantum operations. The Bishop–Gromov bound—a cousin of the focusing lemmas used to prove the Penrose–Hawking black hole singularity theorems—is a differential geometry result that gives an upper bound on the rate of growth of the volume of geodesic balls in terms of the Ricci curvature. Here I apply the Bishop–Gromov bound to Nielsen’s complexity geometry to prove lower bounds on the quantum complexity of a typical unitary. For a broad class of models, the typical complexity is shown to be exponentially large in the number of qubits. This technique gives results that are tighter than all known lower bounds in the literature, as well as establishing lower bounds for a much broader class of complexity geometry metrics than has hitherto been bounded. This method thus realizes the original vision of Nielsen, which was to apply the tools of differential geometry to study quantum complexity.Quantum operations can be considered as points in a high-dimensional space in which distance reflects the similarity of two operations. Applying differential-geometric methods in this picture gives insights into the complexity of quantum systems.
Journal Article
A standard database for drug repositioning
Drug repositioning, the process of discovering, validating, and marketing previously approved drugs for new indications, is of growing interest to academia and industry due to reduced time and costs associated with repositioned drugs. Computational methods for repositioning are appealing because they putatively nominate the most promising candidate drugs for a given indication. Comparing the wide array of computational repositioning methods, however, is a challenge due to inconsistencies in method validation in the field. Furthermore, a common simplifying assumption, that all novel predictions are false, is intellectually unsatisfying and hinders reproducibility. We address this assumption by providing a gold standard database, repoDB, that consists of both true positives (approved drugs), and true negatives (failed drugs). We have made the full database and all code used to prepare it publicly available, and have developed a web application that allows users to browse subsets of the data (
http://apps.chiragjpgroup.org/repoDB/
).
Design Type(s)
data integration objective • database creation objective
Measurement Type(s)
Concomitant Medication Use Indication
Technology Type(s)
digital curation
Factor Type(s)
Machine-accessible metadata file describing the reported data
(ISA-Tab format)
Journal Article
Trauma systems therapy for children and teens
\"For too many traumatized children and their families, chronic stressors such as poverty, substance abuse, and family or community violence--coupled with an overburdened care system/m-/pose seemingly insurmountable barriers to treatment. This empowering book provides a user-friendly blueprint for making the most of limited resources to help those considered the \"toughest cases.\" Evidence-based strategies are presented for effectively integrating individualized treatment with services at the home, school, and community levels. Written in an accessible, modular format with reproducible forms and step-by-step guidelines for assessment and intervention, the approach is grounded in the latest knowledge about child traumatic stress. It has been recognized as a treatment of choice by state mental health agencies nationwide\"-- Provided by publisher.
Book
The evaporation of charged black holes
A
bstract
Charged particle emission from black holes with sufficiently large charge is exponentially suppressed. As a result, such black holes are driven towards extremality by the emission of neutral Hawking radiation. Eventually, an isolated black hole gets close enough to extremality that the gravitational backreaction of a single Hawking photon becomes important, and the quantum field theory in curved spacetime approximation breaks down. To proceed further, we need to use a quantum theory of gravity. We make use of recent progress in our understanding of the quantum-gravitational thermodynamics of near-extremal black holes to compute the corrected spectrum for both neutral and charged Hawking radiation, including the effects of backreaction, as well as greybody factors and metric fluctuations. At low temperatures, large fluctuations in a set of quantum-gravitational (almost) zero modes lead to drastic modifications to neutral particle emission that — in contrast to the semiclassical prediction — ensure the black hole remains subextremal. Relatedly, angular momentum constraints mean that, close enough to extremality, black holes with zero angular momentum can no longer emit individual photons and gravitons; instead, the dominant radiation channel consists of entangled pairs of photons in angular-momentum singlet states. This causes a sudden slowdown in the evaporation rate by a factor of at least 10
700
. We also compute the effects of backreaction and metric fluctuations on the emission of charged particles. Somewhat surprisingly, we find that the semiclassical Schwinger emission rate is essentially unchanged, despite the fact that the emission process leads to large changes in the geometry and thermodynamics of the throat. Our results allow us to present, for the first time, the full history of the evaporation of a large charged black hole. A notable feature of this history is that the black hole alternates between exponentially long epochs of integer and half-integer spin that have radically different cooling rates. This corrects the semiclassical calculation, which gives completely wrong predictions for almost the entire evaporation history, even for the crudest observables like the temperature seen by a thermometer.
Journal Article
Boosting the Biogenesis and Secretion of Mesenchymal Stem Cell-Derived Exosomes
A limitation of using exosomes to their fullest potential is their limited secretion from cells, a major bottleneck to efficient exosome production and application. This is especially true for mesenchymal stem cells (MSCs), which can self-renew but have a limited expansion capacity, undergoing senescence after only a few passages, with exosomes derived from senescent stem cells showing impaired regenerative capacity compared to young cells. Here, we examined the effects of small molecule modulators capable of enhancing exosome secretion from MSCs. The treatment of MSCs with a combination of N-methyldopamine and norepinephrine robustly increased exosome production by three-fold without altering the ability of the MSC exosomes to induce angiogenesis, polarize macrophages to an anti-inflammatory phenotype, or downregulate collagen expression. These small molecule modulators provide a promising means to increase exosome production by MSCs.
Journal Article
The smallest interacting universe
A
bstract
We study a mechanism by which the most basic structures of quantum physics can emerge from the most meager of starting points, a Hilbert space, lacking any preassigned structure such as a tensor decomposition, and a loss function. In a simple toy model of the universe, we hypothesize a fundamental loss functional for the combined Hamiltonian and quantum state, and then minimize this loss functional by gradient descent. We find that this minimization gives rise to a co-emergence of locality, i.e. a tensor product structure simultaneously respected by both the Hamiltonian and the state, suggesting that locality can emerge by a process analogous to spontaneous symmetry breaking. We discuss the relevance of this program to the arrow of time problem.
In our toy model, we interpret the emergence of a tensor factorization as the appearance of individual degrees of freedom within a previously undifferentiated (raw) Hilbert space. Earlier work [
5
,
6
] looked at the emergence of locality in Hamiltonians only, and in that context found strong numerical confirmation of the hypothesis that raw Hilbert spaces of dim =
n
are unstable and prefer to settle on tensor factorization when
n
is not prime, expressing, for example,
n
=
pq
, and in [
6
] even primes were seen to “factor” after first shedding a small summand, e.g. 7 = 1 + 2 · 3. This was found in the context of a rather general potential functional
F
on the space of metrics {
g
ij
} on
su
(
n
), the Lie algebra of symmetries. This emergence of qunits through operator-level spontaneous symmetry breaking (SSB) may help us understand why the world seems to consist of myriad interacting degrees of freedom. But understanding why the universe has an initial Hamiltonian
H
0
with a many-body structure is of limited conceptual value unless the initial state, ∣
ψ
0
〉, is also structured by this tensor decomposition. Here we adapt
F
to become a functional on {
g
, |
ψ
0
〉} = (metrics)
×
(initial states), and find SSB now produces a conspiracy between
g
and ∣
ψ
0
〉, where they simultaneously attain low entropy by jointly settling on the same qubit decomposition. Extreme scaling of the computational problem has confined us to studying ℂ
4
breaking to ℂ
2
⊗ ℂ
2
and ℂ
8
breaking to ℂ
2
⊗ ℂ
4
or ℂ
2
⊗ ℂ
2
⊗ ℂ
2
.
Journal Article