140 research outputs found
Rotational dynamics of CO solvated in small He clusters: a quantum Monte Carlo study
The rotational dynamics of CO single molecules solvated in small He clusters
(CO@He_N) has been studied using Reptation Quantum Monte Carlo for cluster
sizes up to N=30. Our results are in good agreement with the roto-vibrational
features of the infrared spectrum recently determined for this system, and
provide a deep insight into the relation between the structure of the cluster
and its dynamics. Simulations for large N also provide a prediction of the
effective moment of inertia of CO in the He nano-droplet regime, which has not
been measured so far
Rotational dynamics of molecular impurities solvated in 4He clusters. A computational study based on reptation quantum Monte Carlo
The thesis is organized as follows: in the first chapter we provide a short description
of the scenario which frames our work. Some significant experiments
are presented, together with the questions raised by them, the theoretical investigations
they stimulated, and the open issues. The second chapter describes the
reptation quantum Monte Carlo method and its theoretical foundations. Technical
aspects (the choice of the trial functions, the procedure to calculate the cluster
rotational energies) are discussed in third chapter. We also report some studies
on the reptation algorithm. In the fourth chapter we apply RQMC for the interpretation
of the infrared spectra of CO@HeN [5]. The fifth chapter addresses the
problem of the evolution of the rotational dinamics of He solvated rotors toward
the nanodroplet regime; two paradigmatic cases, OCS@HeN and HCN@HeN , are
studied. Our conclusions are drawn in the last chapter
The Information Complexity of Learning Tasks, their Structure and their Distance
We introduce an asymmetric distance in the space of learning tasks, and a
framework to compute their complexity. These concepts are foundational for the
practice of transfer learning, whereby a parametric model is pre-trained for a
task, and then fine-tuned for another. The framework we develop is
non-asymptotic, captures the finite nature of the training dataset, and allows
distinguishing learning from memorization. It encompasses, as special cases,
classical notions from Kolmogorov complexity, Shannon, and Fisher Information.
However, unlike some of those frameworks, it can be applied to large-scale
models and real-world datasets. Our framework is the first to measure
complexity in a way that accounts for the effect of the optimization scheme,
which is critical in Deep Learning
Biophysical and biological contributions of polyamine-coated carbon nanotubes and bidimensional buckypapers in the delivery of miRNAs to human cells
Recent findings in nanomedicine have revealed that carbon nanotubes (CNTs) can be used as potential drug carriers, therapeutic agents and diagnostics tools. Moreover, due to their ability to cross cellular membranes, their nanosize dimension, high surface area and relatively good biocompatibility, CNTs have also been employed as a novel gene delivery vector system. In our previous work, we functionalized CNTs with two polyamine polymers, polyethyleneimine (PEI) and polyamidoamine dendrimer (PAMAM). These compounds have low cytotoxicity, ability to conjugate microRNAs (such as miR-503) and, at the same time, transfect efficiently endothelial cells. The parameters contributing to the good efficiency of transfection that we observed were not investigated in detail. In fact, the diameter and length of CNTs are important parameters to be taken into account when evaluating the effects on drug delivery efficiency. In order to investigate the biophysical and biological contributions of polymer-coated CNTs in delivery of miRNAs to human cells, we decided to investigate three different preparations, characterized by different dimensions and aspect ratios. In particular, we took into account very small CNTs, a suspension of CNTs starting from the commercial product and a 2D material based on CNTs (ie, buckypapers [BPs]) to examine the transfection efficiency of a rigid scaffold. In conclusion, we extensively investigated the biophysical and biological contributions of polyamine-coated CNTs and bidimensional BPs in the delivery of miRNAs to human cells, in order to optimize the transfection efficiency of these compounds to be employed as efficient drug delivery vectors in biomedical applications
Short report: autistic gastrointestinal and eating symptoms treated with secretin: a subtype of autism
Pervasive Developmental Disorders (PDD) are chronic, lifelong disorders for which there is as yet no effective cure, and medical management remains a challenge for clinicians. The current report describes two patients affected by autistic disorder with associated gastrointestinal symptoms. They received multiple doses of intravenous secretin for a six-month period and were assessed with several specific outcome measures to evaluate drug effect. The administration of secretin led to some significant and lasting improvement in only one case. Gastroesophageal reflux may contribute to some of the behavioural problems and explain the effect of secretin since its suppressive effect on gastric secretion is well known. It is also true that autistic children with gastroesophageal reflux and a higher IQ could constitute a subtype which responds to secretin administration and that could be labelled as a "gastrointestinal subtype"
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\`A-la-carte Prompt Tuning (APT): Combining Distinct Data Via Composable Prompting
We introduce \`A-la-carte Prompt Tuning (APT), a transformer-based scheme to
tune prompts on distinct data so that they can be arbitrarily composed at
inference time. The individual prompts can be trained in isolation, possibly on
different devices, at different times, and on different distributions or
domains. Furthermore each prompt only contains information about the subset of
data it was exposed to during training. During inference, models can be
assembled based on arbitrary selections of data sources, which we call
"\`a-la-carte learning". \`A-la-carte learning enables constructing bespoke
models specific to each user's individual access rights and preferences. We can
add or remove information from the model by simply adding or removing the
corresponding prompts without retraining from scratch. We demonstrate that
\`a-la-carte built models achieve accuracy within of models trained on
the union of the respective sources, with comparable cost in terms of training
and inference time. For the continual learning benchmarks Split CIFAR-100 and
CORe50, we achieve state-of-the-art performance.Comment: 13 pages, 4 figures, 8 table
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