16,806 research outputs found
A hybrid quantum algorithm to detect conical intersections
Conical intersections are topologically protected crossings between the
potential energy surfaces of a molecular Hamiltonian, known to play an
important role in chemical processes such as photoisomerization and
non-radiative relaxation. They are characterized by a non-zero Berry phase,
which is a topological invariant defined on a closed path in atomic coordinate
space, taking the value when the path encircles the intersection
manifold. In this work, we show that for real molecular Hamiltonians, the Berry
phase can be obtained by tracing a local optimum of a variational ansatz along
the chosen path and estimating the overlap between the initial and final state
with a control-free Hadamard test. Moreover, by discretizing the path into
points, we can use single Newton-Raphson steps to update our state
non-variationally. Finally, since the Berry phase can only take two discrete
values (0 or ), our procedure succeeds even for a cumulative error bounded
by a constant; this allows us to bound the total sampling cost and to readily
verify the success of the procedure. We demonstrate numerically the application
of our algorithm on small toy models of the formaldimine molecule
(\ce{H2C=NH}).Comment: 15 + 10 pages, 4 figure
Safe Zeroth-Order Optimization Using Quadratic Local Approximations
This paper addresses black-box smooth optimization problems, where the
objective and constraint functions are not explicitly known but can be queried.
The main goal of this work is to generate a sequence of feasible points
converging towards a KKT primal-dual pair. Assuming to have prior knowledge on
the smoothness of the unknown objective and constraints, we propose a novel
zeroth-order method that iteratively computes quadratic approximations of the
constraint functions, constructs local feasible sets and optimizes over them.
Under some mild assumptions, we prove that this method returns an -KKT
pair (a property reflecting how close a primal-dual pair is to the exact KKT
condition) within iterations. Moreover, we numerically show
that our method can achieve faster convergence compared with some
state-of-the-art zeroth-order approaches. The effectiveness of the proposed
approach is also illustrated by applying it to nonconvex optimization problems
in optimal control and power system operation.Comment: arXiv admin note: text overlap with arXiv:2211.0264
Dual dynamic programming for stochastic programs over an infinite horizon
We consider a dual dynamic programming algorithm for solving stochastic
programs over an infinite horizon. We show non-asymptotic convergence results
when using an explorative strategy, and we then enhance this result by reducing
the dependence of the effective planning horizon from quadratic to linear. This
improvement is achieved by combining the forward and backward phases from dual
dynamic programming into a single iteration. We then apply our algorithms to a
class of problems called hierarchical stationary stochastic programs, where the
cost function is a stochastic multi-stage program. The hierarchical program can
model problems with a hierarchy of decision-making, e.g., how long-term
decisions influence day-to-day operations. We show that when the subproblems
are solved inexactly via a dynamic stochastic approximation-type method, the
resulting hierarchical dual dynamic programming can find approximately optimal
solutions in finite time. Preliminary numerical results show the practical
benefits of using the explorative strategy for solving the Brazilian
hydro-thermal planning problem and economic dispatch, as well as the potential
to exploit parallel computing.Comment: 45 pages. New experiments for hierarchical problem and writing
update
Plateau-reduced Differentiable Path Tracing
Current differentiable renderers provide light transport gradients with
respect to arbitrary scene parameters. However, the mere existence of these
gradients does not guarantee useful update steps in an optimization. Instead,
inverse rendering might not converge due to inherent plateaus, i.e., regions of
zero gradient, in the objective function. We propose to alleviate this by
convolving the high-dimensional rendering function that maps scene parameters
to images with an additional kernel that blurs the parameter space. We describe
two Monte Carlo estimators to compute plateau-free gradients efficiently, i.e.,
with low variance, and show that these translate into net-gains in optimization
error and runtime performance. Our approach is a straightforward extension to
both black-box and differentiable renderers and enables optimization of
problems with intricate light transport, such as caustics or global
illumination, that existing differentiable renderers do not converge on.Comment: Accepted to CVPR 2023. Project page and interactive demos at
https://mfischer-ucl.github.io/prdpt
Compressed-VFL: Communication-Efficient Learning with Vertically Partitioned Data
We propose Compressed Vertical Federated Learning (C-VFL) for
communication-efficient training on vertically partitioned data. In C-VFL, a
server and multiple parties collaboratively train a model on their respective
features utilizing several local iterations and sharing compressed intermediate
results periodically. Our work provides the first theoretical analysis of the
effect message compression has on distributed training over vertically
partitioned data. We prove convergence of non-convex objectives at a rate of
when the compression error is bounded over the course
of training. We provide specific requirements for convergence with common
compression techniques, such as quantization and top- sparsification.
Finally, we experimentally show compression can reduce communication by over
without a significant decrease in accuracy over VFL without compression
A direct-laser-written heart-on-a-chip platform for generation and stimulation of engineered heart tissues
In this dissertation, we first develop a versatile microfluidic heart-on-a-chip model to generate 3D-engineered human cardiac microtissues in highly-controlled microenvironments. The platform, which is enabled by direct laser writing (DLW), has tailor-made attachment sites for cardiac microtissues and comes with integrated strain actuators and force sensors. Application of external pressure waves to the platform results in controllable time-dependent forces on the microtissues. Conversely, oscillatory forces generated by the microtissues are transduced into measurable electrical outputs. After characterization of the responsivity of the transducers, we demonstrate the capabilities of this platform by studying the response of cardiac microtissues to prescribed mechanical loading and pacing.
Next, we tune the geometry and mechanical properties of the platform to enable parametric studies on engineered heart tissues. We explore two geometries: a rectangular seeding well with two attachment sites, and a stadium-like seeding well with six attachment sites. The attachment sites are placed symmetrically in the longitudinal direction. The former geometry promotes uniaxial contraction of the tissues; the latter additionally induces diagonal
fiber alignment. We systematically increase the length for both configurations and observe a positive correlation between fiber alignment at the center of the microtissues and tissue length. However, progressive thinning and “necking” is also observed, leading to the failure of longer tissues over time. We use the DLW technique to improve the platform, softening
the mechanical environment and optimizing the attachment sites for generation of stable microtissues at each length and geometry. Furthermore, electrical pacing is incorporated into the platform to evaluate the functional dynamics of stable microtissues over the entire range of physiological heart rates. Here, we typically observe a decrease in active force and contraction duration as a function of frequency.
Lastly, we use a more traditional ?TUG platform to demonstrate the effects of subthreshold electrical pacing on the rhythm of the spontaneously contracting cardiac microtissues. Here, we observe periodic M:N patterns, in which there are ? cycles of stimulation for every ? tissue contractions. Using electric field amplitude, pacing frequency, and homeostatic beating frequencies of the tissues, we provide an empirical map for predicting the emergence of these rhythms
Association of adverse childhood experiences with the diagnosis and severity of obstructive sleep apnea
BACKGROUND: Obstructive Sleep Apnea (OSA) is a very common disease characterized by brief episodes of airway collapse and low oxygen during sleep. Many years of research on OSA have shown that social determinants of health, such as race, income, zip code, and parental education level lead to varied levels of disease prevalence and severity among different populations. It has been shown very clearly that low-income African-American children have the highest prevalence and most severe outcomes of OSA. However, there is one very important component of health that has not been evaluated in conjunction with OSA: childhood trauma.
To assess for childhood trauma, physicians often use the Adverse Childhood Experiences (ACE) QUESTIONNAIRE. This series of questions has been used in numerous medical specialties, including primary care, oncology, pulmonology, general surgery, and obstetrics/gynecology, for decades to evaluate patients for childhood trauma before the age of 18. This survey not only allows clinicians to provide trauma-informed care to their patients, but also serves as a reminder to address both the social and physical aspects of disease when treating a patient, as trauma has been shown to have detrimental effects on long-term health. Over two decades of research have shown that an increased number of ACEs before the age of 18 leads to worse outcomes in a wide variety of diseases, many of which are some of the leading causes of morbidity and mortality in the United States. However, no studies to date have used the ACE questionnaire to evaluate disease and surgical outcomes in the field of otolaryngology (ENT), one of the medical specialties in which patients with OSA are treated and followed. Given the prevalence of OSA nationwide among adults and children, it is crucial to begin examining whether childhood trauma leads to worse disease outcomes in OSA.
OBJECTIVE: To conduct a comprehensive literature review of research done on both pediatric OSA and the effects of childhood trauma on disease outcomes for some of most common causes of morbidity and mortality in the United States. An additional objective is to show, using data from the Kids Inpatient Database, associations between various demographic factors and diagnosis with OSA requiring an adenotonsillectomy.
METHODS: For the literature review, a PubMed search was conducted on both aforementioned topics using various keywords and MeSH terms to narrow down the search. Reference lists of relevant papers were also used to find other relevant papers. For the empirical data, the Kids’ Inpatient Database, a national database created by the Healthcare Cost and Utilization Project and Agency for Healthcare Research and Quality, was used. There have been many version of this database, but the most recent version from 2016 was used for this study. Due to the COVID-19 pandemic-related restrictions, we were not able to administer the ACE Questionnaire to patients with obstructive sleep apnea as originally planned.
RESULTS: The literature review on pediatric OSA showed that the main risk factors for developing severe OSA are adenotonsillar hypertrophy, African-American race, low socioeconomic status/low income, and obesity. Other important risk factors include preterm birth, male sex, and craniofacial anomalies. The literature review on childhood trauma showed that adults over the age of 18 who endorsed more adverse experiences on the ACE questionnaire consistently had worse disease outcomes in chronic illnesses such as ischemic heart disease, chronic obstructive pulmonary disease, and some cancers. The results from the Kids Inpatient Database showed that Black children had the highest odds of developing OSA and requiring a tonsillectomy. Additionally, the Kids Inpatient Database shed light on the odds of having a tonsillectomy based on income quartile, showing that children of higher income quartiles are more likely to receive surgery.
CONCLUSIONS: Many years of research have shown both that social determinants of health such as income, race, and socioeconomic status are associated with severity of obstructive sleep apnea, and that increased childhood trauma is often associated with worse disease outcomes in a wide variety of chronic illnesses. However, a very important next step in research on these topics is to combine them to assess whether increased childhood trauma also correlates with increased severity of OSA
Estudo da remodelagem reversa miocárdica através da análise proteómica do miocárdio e do líquido pericárdico
Valve replacement remains as the standard therapeutic option for aortic
stenosis patients, aiming at abolishing pressure overload and triggering
myocardial reverse remodeling. However, despite the instant hemodynamic
benefit, not all patients show complete regression of myocardial hypertrophy,
being at higher risk for adverse outcomes, such as heart failure. The current
comprehension of the biological mechanisms underlying an incomplete reverse
remodeling is far from complete. Furthermore, definitive prognostic tools and
ancillary therapies to improve the outcome of the patients undergoing valve
replacement are missing. To help abridge these gaps, a combined myocardial
(phospho)proteomics and pericardial fluid proteomics approach was followed,
taking advantage of human biopsies and pericardial fluid collected during
surgery and whose origin anticipated a wealth of molecular information
contained therein.
From over 1800 and 750 proteins identified, respectively, in the myocardium
and in the pericardial fluid of aortic stenosis patients, a total of 90 dysregulated
proteins were detected. Gene annotation and pathway enrichment analyses,
together with discriminant analysis, are compatible with a scenario of increased
pro-hypertrophic gene expression and protein synthesis, defective ubiquitinproteasome system activity, proclivity to cell death (potentially fed by
complement activity and other extrinsic factors, such as death receptor
activators), acute-phase response, immune system activation and fibrosis.
Specific validation of some targets through immunoblot techniques and
correlation with clinical data pointed to complement C3 β chain, Muscle Ring
Finger protein 1 (MuRF1) and the dual-specificity Tyr-phosphorylation
regulated kinase 1A (DYRK1A) as potential markers of an incomplete
response. In addition, kinase prediction from phosphoproteome data suggests
that the modulation of casein kinase 2, the family of IκB kinases, glycogen
synthase kinase 3 and DYRK1A may help improve the outcome of patients
undergoing valve replacement. Particularly, functional studies with DYRK1A+/-
cardiomyocytes show that this kinase may be an important target to treat
cardiac dysfunction, provided that mutant cells presented a different response
to stretch and reduced ability to develop force (active tension).
This study opens many avenues in post-aortic valve replacement reverse
remodeling research. In the future, gain-of-function and/or loss-of-function
studies with isolated cardiomyocytes or with animal models of aortic bandingdebanding will help disclose the efficacy of targeting the surrogate therapeutic
targets. Besides, clinical studies in larger cohorts will bring definitive proof of
complement C3, MuRF1 and DYRK1A prognostic value.A substituição da válvula aórtica continua a ser a opção terapêutica de
referência para doentes com estenose aórtica e visa a eliminação da
sobrecarga de pressão, desencadeando a remodelagem reversa miocárdica.
Contudo, apesar do benefício hemodinâmico imediato, nem todos os pacientes
apresentam regressão completa da hipertrofia do miocárdio, ficando com maior
risco de eventos adversos, como a insuficiência cardíaca. Atualmente, os
mecanismos biológicos subjacentes a uma remodelagem reversa incompleta
ainda não são claros. Além disso, não dispomos de ferramentas de
prognóstico definitivos nem de terapias auxiliares para melhorar a condição
dos pacientes indicados para substituição da válvula. Para ajudar a resolver
estas lacunas, uma abordagem combinada de (fosfo)proteómica e proteómica
para a caracterização, respetivamente, do miocárdio e do líquido pericárdico
foi seguida, tomando partido de biópsias e líquidos pericárdicos recolhidos em
ambiente cirúrgico.
Das mais de 1800 e 750 proteínas identificadas, respetivamente, no miocárdio
e no líquido pericárdico dos pacientes com estenose aórtica, um total de 90
proteínas desreguladas foram detetadas. As análises de anotação de genes,
de enriquecimento de vias celulares e discriminativa corroboram um cenário de
aumento da expressão de genes pro-hipertróficos e de síntese proteica, um
sistema ubiquitina-proteassoma ineficiente, uma tendência para morte celular
(potencialmente acelerada pela atividade do complemento e por outros fatores
extrínsecos que ativam death receptors), com ativação da resposta de fase
aguda e do sistema imune, assim como da fibrose.
A validação de alguns alvos específicos através de immunoblot e correlação
com dados clínicos apontou para a cadeia β do complemento C3, a Muscle
Ring Finger protein 1 (MuRF1) e a dual-specificity Tyr-phosphoylation
regulated kinase 1A (DYRK1A) como potenciais marcadores de uma resposta
incompleta. Por outro lado, a predição de cinases a partir do fosfoproteoma,
sugere que a modulação da caseína cinase 2, a família de cinases do IκB, a
glicogénio sintase cinase 3 e da DYRK1A pode ajudar a melhorar a condição
dos pacientes indicados para intervenção. Em particular, a avaliação funcional
de cardiomiócitos DYRK1A+/- mostraram que esta cinase pode ser um alvo
importante para tratar a disfunção cardíaca, uma vez que os miócitos mutantes
responderam de forma diferente ao estiramento e mostraram uma menor
capacidade para desenvolver força (tensão ativa).
Este estudo levanta várias hipóteses na investigação da remodelagem reversa.
No futuro, estudos de ganho e/ou perda de função realizados em
cardiomiócitos isolados ou em modelos animais de banding-debanding da
aorta ajudarão a testar a eficácia de modular os potenciais alvos terapêuticos
encontrados. Além disso, estudos clínicos em coortes de maior dimensão
trarão conclusões definitivas quanto ao valor de prognóstico do complemento
C3, MuRF1 e DYRK1A.Programa Doutoral em Biomedicin
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Co-design As Healing: Exploring The Experiences Of Participants Facing Mental Health Problems
This thesis is an exploration of the healing role of co-design in mental health. Although co-design projects conducted within mental health settings are rising, existing literature tends to focus on the object of design and its outcomes while the experiences of participants per se remain largely unexplored. The guiding research question of this study is not how we design things that improve mental health, but how co-designing, as an act, might do so.
The thesis presents two projects that were organized in collaboration with the mental health charity Islington Mind and the Psychosis Therapy Project (PTP) in London.
The project at Islington Mind used a structured design process inviting participants to design for wellbeing. A case study analysis provides insights on how participants were impacted, summarizing key challenges and opportunities.
The design at PTP worked towards creating a collective brief in an emergent fashion, finally culminating in a board game. The experiences of participants were explored through Interpretative Phenomenological Analysis (IPA), using semi-structured interview data. The analysis served to identify key themes characterising the experience of co-design such as contributing, connecting, thinking and intentioning. In addition, a mixed-methods analysis of questionnaires and interview data exploring participants' wellbeing, showed that all participants who engaged fairly consistently in the project improved after the project ended, although some participants' scores returned to baseline six months later.
Reflecting on both projects, an approach to facilitation within mental health is outlined, detailing how the dimensions of weaving and layered participation, nurturing mattering and facilitating attitudes interlace. This contribution raises awareness of tacit dimensions in the practice of facilitation, articulating the nuances of how to encourage and sustain meaningful and ethical engagement and offering insights into a range of tools. It highlights the importance of remaining reflexive in relation to attitudes and emotions and discusses practical methodological and ethical challenges and ways to resolve them which can be of benefit to researchers embarking on a similar journey.
The thesis also offers detailed insights on how methodologies from different fields were integrated into a whole, arguing for transparency and reflexivity about epistemological assumptions, and how underlying paradigms shift in an interdisciplinary context.
Based on the overall findings, the thesis makes a case for considering design as healing (or a designerly way of healing), highlighting implications at a systems, social and individual level. It makes an original contribution to our understanding of design, highlighting its healing character, and proposes a new way to support mental health. The participants in this study not only had increased their own wellbeing through co-designing, but were also empowered and contributed towards healing the world. Hence, the thesis argues for a unique, holistic perspective of design and mental health, recognizing the interconnectedness of the individual, social and systemic dimensions of the healing processes that are ignited
Underwater optical wireless communications in turbulent conditions: from simulation to experimentation
Underwater optical wireless communication (UOWC) is a technology that aims to apply high speed optical wireless communication (OWC) techniques to the underwater channel. UOWC has the potential to provide high speed links over relatively short distances as part of a hybrid underwater network, along with radio frequency (RF) and underwater acoustic communications (UAC) technologies. However, there are some difficulties involved in developing a reliable UOWC link, namely, the complexity of the channel. The main focus throughout this thesis is to develop a greater understanding of the effects of the UOWC channel, especially underwater turbulence. This understanding is developed from basic theory through to simulation and experimental studies in order to gain a holistic understanding of turbulence in the UOWC channel.
This thesis first presents a method of modelling optical underwater turbulence through simulation that allows it to be examined in conjunction with absorption and scattering. In a stationary channel, this turbulence induced scattering is shown to cause and increase both spatial and temporal spreading at the receiver plane. It is also demonstrated using the technique presented that the relative impact of turbulence on a received signal is lower in a highly scattering channel, showing an in-built resilience of these channels. Received intensity distributions are presented confirming that fluctuations in received power from this method follow the commonly used Log-Normal fading model. The impact of turbulence - as measured using this new modelling framework - on link performance, in terms of maximum achievable data rate and bit error rate is equally investigated.
Following that, experimental studies comparing both the relative impact of turbulence induced scattering on coherent and non-coherent light propagating through water and the relative impact of turbulence in different water conditions are presented. It is shown that the scintillation index increases with increasing temperature inhomogeneity in the underwater channel. These results indicate that a light beam from a non-coherent source has a greater resilience to temperature inhomogeneity induced turbulence effect in an underwater channel. These results will help researchers in simulating realistic channel conditions when modelling a light emitting diode (LED) based intensity modulation with direct detection (IM/DD) UOWC link.
Finally, a comparison of different modulation schemes in still and turbulent water conditions is presented. Using an underwater channel emulator, it is shown that pulse position modulation (PPM) and subcarrier intensity modulation (SIM) have an inherent resilience to turbulence induced fading with SIM achieving higher data rates under all conditions. The signal processing technique termed pair-wise coding (PWC) is applied to SIM in underwater optical wireless communications for the first time. The performance of PWC is compared with the, state-of-the-art, bit and power loading optimisation algorithm. Using PWC, a maximum data rate of 5.2 Gbps is achieved in still water conditions
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