150 research outputs found
Early phases of different types of isolated neutron star
Two Galactic isolated strong X-ray pulsars seem to be in the densest
environments compared to other types of Galactic pulsar. X-ray pulsar
J1846-0258 can be in an early phase of anomalous X-ray pulsars and soft gamma
repeaters if its average braking index is ~1.8-2.0. X-ray pulsar J1811-1925
must have a very large average braking index (n~11) if this pulsar was formed
by SN 386AD. This X-ray pulsar can be in an early phase of evolution of the
radio pulsars located in the region P~50-150 ms and \.{P}~10
s/s of the P-\.{P} diagram. X-ray/radio pulsar J0540-69 seems to be evolving in
the direction to the dim isolated thermal neutron star region on the P-\.{P}
diagram. Possible progenitors of different types of neutron star are also
discussed.Comment: to appear in the International Journal of Modern Physics
Exploiting Pretrained Biochemical Language Models for Targeted Drug Design
Motivation: The development of novel compounds targeting proteins of interest
is one of the most important tasks in the pharmaceutical industry. Deep
generative models have been applied to targeted molecular design and have shown
promising results. Recently, target-specific molecule generation has been
viewed as a translation between the protein language and the chemical language.
However, such a model is limited by the availability of interacting
protein-ligand pairs. On the other hand, large amounts of unlabeled protein
sequences and chemical compounds are available and have been used to train
language models that learn useful representations. In this study, we propose
exploiting pretrained biochemical language models to initialize (i.e. warm
start) targeted molecule generation models. We investigate two warm start
strategies: (i) a one-stage strategy where the initialized model is trained on
targeted molecule generation (ii) a two-stage strategy containing a
pre-finetuning on molecular generation followed by target specific training. We
also compare two decoding strategies to generate compounds: beam search and
sampling.
Results: The results show that the warm-started models perform better than a
baseline model trained from scratch. The two proposed warm-start strategies
achieve similar results to each other with respect to widely used metrics from
benchmarks. However, docking evaluation of the generated compounds for a number
of novel proteins suggests that the one-stage strategy generalizes better than
the two-stage strategy. Additionally, we observe that beam search outperforms
sampling in both docking evaluation and benchmark metrics for assessing
compound quality.
Availability and implementation: The source code is available at
https://github.com/boun-tabi/biochemical-lms-for-drug-design and the materials
are archived in Zenodo at https://doi.org/10.5281/zenodo.6832145Comment: 12 pages, to appear in Bioinformatic
Exploring Data-Driven Chemical SMILES Tokenization Approaches to Identify Key Protein-Ligand Binding Moieties
Machine learning models have found numerous successful applications in
computational drug discovery. A large body of these models represents molecules
as sequences since molecular sequences are easily available, simple, and
informative. The sequence-based models often segment molecular sequences into
pieces called chemical words (analogous to the words that make up sentences in
human languages) and then apply advanced natural language processing techniques
for tasks such as drug design, property prediction, and
binding affinity prediction. However, the chemical characteristics and
significance of these building blocks, chemical words, remain unexplored. This
study aims to investigate the chemical vocabularies generated by popular
subword tokenization algorithms, namely Byte Pair Encoding (BPE), WordPiece,
and Unigram, and identify key chemical words associated with protein-ligand
binding. To this end, we build a language-inspired pipeline that treats high
affinity ligands of protein targets as documents and selects key chemical words
making up those ligands based on tf-idf weighting. Further, we conduct case
studies on a number of protein families to analyze the impact of key chemical
words on binding. Through our analysis, we find that these key chemical words
are specific to protein targets and correspond to known pharmacophores and
functional groups. Our findings will help shed light on the chemistry captured
by the chemical words, and by machine learning models for drug discovery at
large.Comment: 16 pages, 11 figures, new computational analysis and extended case
studie
Nano-bioceramic synthesis from tropical sea snail shells (Tiger Cowrie - Cypraea Tigris) with simple chemical treatment
In this study several bioceramic materials (i.e. hydroxyapatite, whitlockite) were prepared by using chemical synthesis method from sea snail shells (Tiger Cowrie - Cypraea Tigris), originated from Pacific Ocean. Marine shells usually present aragonite-calcite structures and generally, complicated and pressurized equipment is necessary to convert these structures into bioceramics. Instead of using complicated systems, a basic ultrasonic equipment and simple chemical synthesis method was used in the process. DTA analysis was performed to calculate the required amount of H3PO4 solution in order to set the appropriate stoichiometric ratio of Ca/P equal to 1.667 for HA bioceramic or to 1.5 for β-TCP bioceramic in the titration. The prepared batches were sintered at 800°C and 400 °C for hydroxyapatite (HA) and β-tri calcium phosphate (β-TCP) forms respectively. X-ray diffraction analysis, scanning electron microscopy (SEM) and infrared observations (FTIR) were implemented for both TCP and HA bioceramics. By applying the chemical synthesis with basic ultrasonic equipment, this study proposes a simple way of production for nano-HA/TCP powders from a natural marine sources
A Twisted Kink Crystal in the Chiral Gross-Neveu model
We present the detailed properties of a self-consistent crystalline chiral
condensate in the massless chiral Gross-Neveu model. We show that a suitable
ansatz for the Gorkov resolvent reduces the functional gap equation, for the
inhomogeneous condensate, to a nonlinear Schr\"odinger equation, which is
exactly soluble. The general crystalline solution includes as special cases all
previously known real and complex condensate solutions to the gap equation.
Furthermore, the associated Bogoliubov-de Gennes equation is also soluble with
this inhomogeneous chiral condensate, and the exact spectral properties are
derived. We find an all-orders expansion of the Ginzburg-Landau effective
Lagrangian and show how the gap equation is solved order-by-order.Comment: 28 pages, 13 figs; v2: new appendix on Eilenberger eq and refs;
version in PR
Micro-connectomics: probing the organization of neuronal networks at the cellular scale.
Defining the organizational principles of neuronal networks at the cellular scale, or micro-connectomics, is a key challenge of modern neuroscience. In this Review, we focus on graph theoretical parameters of micro-connectome topology, often informed by economical principles that conceptually originated with Ramón y Cajal's conservation laws. First, we summarize results from studies in intact small organisms and in samples from larger nervous systems. We then evaluate the evidence for an economical trade-off between biological cost and functional value in the organization of neuronal networks. Various results suggest that many aspects of neuronal network organization are indeed the outcome of competition between these two fundamental selection pressures.This work was supported by the National Institute of Health Research (NIHR) Cambridge Biomedical Research Centre.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by the Nature Publishing Group
Global respiratory syncytial virus–related infant community deaths
Background
Respiratory syncytial virus (RSV) is a leading cause of pediatric death, with >99% of mortality occurring in low- and lower middle-income countries. At least half of RSV-related deaths are estimated to occur in the community, but clinical characteristics of this group of children remain poorly characterized.
Methods
The RSV Global Online Mortality Database (RSV GOLD), a global registry of under-5 children who have died with RSV-related illness, describes clinical characteristics of children dying of RSV through global data sharing. RSV GOLD acts as a collaborative platform for global deaths, including community mortality studies described in this supplement. We aimed to compare the age distribution of infant deaths <6 months occurring in the community with in-hospital.
Results
We studied 829 RSV-related deaths <1 year of age from 38 developing countries, including 166 community deaths from 12 countries. There were 629 deaths that occurred <6 months, of which 156 (25%) occurred in the community. Among infants who died before 6 months of age, median age at death in the community (1.5 months; IQR: 0.8−3.3) was lower than in-hospital (2.4 months; IQR: 1.5−4.0; P < .0001). The proportion of neonatal deaths was higher in the community (29%, 46/156) than in-hospital (12%, 57/473, P < 0.0001).
Conclusions
We observed that children in the community die at a younger age. We expect that maternal vaccination or immunoprophylaxis against RSV will have a larger impact on RSV-related mortality in the community than in-hospital. This case series of RSV-related community deaths, made possible through global data sharing, allowed us to assess the potential impact of future RSV vaccines
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