508 research outputs found
The effects of short-lived radionuclides and porosity on the early thermo-mechanical evolution of planetesimals
The thermal history and internal structure of chondritic planetesimals,
assembled before the giant impact phase of chaotic growth, potentially yield
important implications for the final composition and evolution of terrestrial
planets. These parameters critically depend on the internal balance of heating
versus cooling, which is mostly determined by the presence of short-lived
radionuclides (SLRs), such as aluminum-26 and iron-60, as well as the heat
conductivity of the material. The heating by SLRs depends on their initial
abundances, the formation time of the planetesimal and its size. It has been
argued that the cooling history is determined by the porosity of the granular
material, which undergoes dramatic changes via compaction processes and tends
to decrease with time. In this study we assess the influence of these
parameters on the thermo-mechanical evolution of young planetesimals with both
2D and 3D simulations. Using the code family I2ELVIS/I3ELVIS we have run
numerous 2D and 3D numerical finite-difference fluid dynamic models with
varying planetesimal radius, formation time and initial porosity. Our results
indicate that powdery materials lowered the threshold for melting and
convection in planetesimals, depending on the amount of SLRs present. A subset
of planetesimals retained a powdery surface layer which lowered the thermal
conductivity and hindered cooling. The effect of initial porosity was small,
however, compared to those of planetesimal size and formation time, which
dominated the thermo-mechanical evolution and were the primary factors for the
onset of melting and differentiation. We comment on the implications of this
work concerning the structure and evolution of these planetesimals, as well as
their behavior as possible building blocks of terrestrial planets.Comment: 19 pages, 11 figures, 5 tables; accepted for publication in Icarus;
for associated video files, see http://timlichtenberg.net/2015_porosity.html
or http://dx.doi.org/10.1016/j.icarus.2016.03.00
The Interval [0,1] Admits no Functorial Embedding into a Finite-Dimensional or Metrizable Topological Group
An embedding X ⊂ G of a topological space X into a topological group G is called functorial if every homeomorphism of X extends
to a continuous group homomorphism of G. It is shown that the interval [0, 1] admits no functorial embedding into a finite-dimensional or metrizable
topological group
The Impact of Video Conference on Orthopaedic Resident Education: A Survey
Background: Covid and required social distancing has accelerated the use of video conferencing. We hypothesized that residents and faculty would be less receptive to the video lecture format and prefer traditional didactic methods.
Methods: A 16-question anonymous survey was distributed nationally to orthopaedic residents and faculty. The survey collected basic demographic information such as, level in training, gender, and age. We then asked the respondent to rate their agreement or disagreement with 8 statements on a Likert scale (1-5) about video conferencing regarding orthopedic education. Likert scale responses were evaluated using basic descriptive statistics. Respondents were divided into groups of faculty and residents. Residents were subdivided into junior residents (PGY-1s and PGY-2s) and senior residents (PGY-3s, PGY-4s, and PGY-5s). A Wilcoxon rank sum test was used for the Likert scale type questions and a Fisher’s exact test was used for the pros/cons questions to evaluate for a difference in responses between groups.
Results: A total of 123 residents or faculty responded to the survey. One was excluded because only the demographics section was completed, leaving 122 respondents. Respondents were found to prefer the traditional didactics compared to the new virtual format (p
Conclusions: Orthopaedic residents and faculty do not prefer the new virtual didactic format compared to the traditional approach.
Level of Evidence: Level IV Cross-Sectional Stud
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PLZF Controls the Expression of a Limited Number of Genes Essential for NKT Cell Function
Natural killer (NKT) T cells exhibit tissue distribution, surface phenotype, and functional responses that are strikingly different from those of conventional T cells. The transcription factor PLZF is responsible for most of these properties, as its ectopic expression in conventional T cells is sufficient to confer to them an NKT-like phenotype. The molecular program downstream of PLZF, however, is largely unexplored. Here we report that PLZF regulates the expression of a surprisingly small set of genes, many with known immune functions. This includes several established components of the NKT cell developmental program. Expression of the transcriptional regulators Id2, previously shown to be required for iNKT cell survival in the liver and c-Maf, which shapes the NKT cytokine profile, was compromised in PLZF-deficient cells. Ectopic expression of c-Maf complemented the cells’ defect in producing IL-4 and IL-10. PLZF also induced a program of cell surface receptors which shape the NKT cell’s response to external stimuli, including the costimulatory receptor ICOS and the cytokine receptors IL12rb1 and IL18r1. As an ensemble, the known functions of the molecules whose expression is affected by PLZF explain many defects observed in NKT cells
Impact splash chondrule formation during planetesimal recycling
Chondrules are the dominant bulk silicate constituent of chondritic
meteorites and originate from highly energetic, local processes during the
first million years after the birth of the Sun. So far, an astrophysically
consistent chondrule formation scenario, explaining major chemical, isotopic
and textural features, remains elusive. Here, we examine the prospect of
forming chondrules from planetesimal collisions. We show that intensely melted
bodies with interior magma oceans became rapidly chemically equilibrated and
physically differentiated. Therefore, collisional interactions among such
bodies would have resulted in chondrule-like but basaltic spherules, which are
not observed in the meteoritic record. This inconsistency with the expected
dynamical interactions hints at an incomplete understanding of the planetary
growth regime during the protoplanetary disk phase. To resolve this conundrum,
we examine how the observed chemical and isotopic features of chondrules
constrain the dynamical environment of accreting chondrite parent bodies by
interpreting the meteoritic record as an impact-generated proxy of
planetesimals that underwent repeated collision and reaccretion cycles. Using a
coupled evolution-collision model we demonstrate that the vast majority of
collisional debris feeding the asteroid main belt must be derived from
planetesimals which were partially molten at maximum. Therefore, the precursors
of chondrite parent bodies either formed primarily small, from sub-canonical
aluminum-26 reservoirs, or collisional destruction mechanisms were efficient
enough to shatter planetesimals before they reached the magma ocean phase.
Finally, we outline the window in parameter space for which chondrule formation
from planetesimal collisions can be reconciled with the meteoritic record and
how our results can be used to further constrain early solar system dynamics.Comment: 20 pages, 11 figures, 2 tables; accepted for publication in Icarus;
associated blog article at goo.gl/5bDqG
Goal-Directed Acupuncture in Sports—Placebo or Doping?
The modern pentathlon (MP), sports discipline including fencing, swimming, steeplechase and a cross-country run, requires a rapid change of central nervous and peripheral neuromuscular activity from one sport to another in order to achieve the best possible results. We describe the case where a top MP athlete was supported by a program of acupoint stimulation, which was directed to relieve the symptoms, preventing him from effective performance. Although the fact of acupoint stimulation was associated with improvement of his results, other factors like training effect, placebo and nonspecific physiological effects and their mechanisms in sports are discussed in a literature review. The popularity of complementary and alternative medicine methods among the athletes raises the question of their potential misuse as a doping in competitive sports
Methods of Administering Superimposed High-Frequency Jet Ventilation and the Associated Risk for Aspiration in a Model of Tracheal Bleeding
Background: To determine the suitability of different superimposed high-frequency jet ventilation (SHFJV) application methods during tracheal bleeding. Objective: To determine the effect of SHFJV on the aspiration of blood during tracheal bleeding. Methods: A test lung was ventilated using SHFJV via a rigid endoscope, a jet laryngoscope and a 4-lumen jet catheter. Packed red blood cells (PRBCs) were injected into the artificial trachea caudally to the rigid endoscope and jet laryngoscope ventilation, and both caudally and cranially during ventilation via the 4-lumen jet catheter, and the migration of PRBCs during ventilation was studied using continuous video recording. Results: Migration of blood into the lower respiratory tract did not occur during SHFJV via the rigid endoscope and jet laryngoscope and via the 4-lumen jet catheter with the bleeding caudal to ventilation source. If the bleeding was cranial to the 4-lumen jet catheter ventilation, migration of blood into the lower respiratory tract was seen when reflux of blood reached the entrainment area. From this area, blood is transported within the jet stream into the lower respiratory tract. Conclusions: SHFJV protects the lower respiratory tract from blood aspiration in case of tracheal bleeding. During SHFJV via the 4-lumen jet catheter, aspiration of blood only occurs if bleeding is localized cranial to the 4-lumen jet catheter ventilation. In case of heavy tracheal bleeding, the jet sources should be positioned cranial to the site of bleeding
A Comprehensive Review of Data-Driven Co-Speech Gesture Generation
Gestures that accompany speech are an essential part of natural and efficient
embodied human communication. The automatic generation of such co-speech
gestures is a long-standing problem in computer animation and is considered an
enabling technology in film, games, virtual social spaces, and for interaction
with social robots. The problem is made challenging by the idiosyncratic and
non-periodic nature of human co-speech gesture motion, and by the great
diversity of communicative functions that gestures encompass. Gesture
generation has seen surging interest recently, owing to the emergence of more
and larger datasets of human gesture motion, combined with strides in
deep-learning-based generative models, that benefit from the growing
availability of data. This review article summarizes co-speech gesture
generation research, with a particular focus on deep generative models. First,
we articulate the theory describing human gesticulation and how it complements
speech. Next, we briefly discuss rule-based and classical statistical gesture
synthesis, before delving into deep learning approaches. We employ the choice
of input modalities as an organizing principle, examining systems that generate
gestures from audio, text, and non-linguistic input. We also chronicle the
evolution of the related training data sets in terms of size, diversity, motion
quality, and collection method. Finally, we identify key research challenges in
gesture generation, including data availability and quality; producing
human-like motion; grounding the gesture in the co-occurring speech in
interaction with other speakers, and in the environment; performing gesture
evaluation; and integration of gesture synthesis into applications. We
highlight recent approaches to tackling the various key challenges, as well as
the limitations of these approaches, and point toward areas of future
development.Comment: Accepted for EUROGRAPHICS 202
A meta-analysis of Boolean network models reveals design principles of gene regulatory networks
Gene regulatory networks (GRNs) describe how a collection of genes governs
the processes within a cell. Understanding how GRNs manage to consistently
perform a particular function constitutes a key question in cell biology. GRNs
are frequently modeled as Boolean networks, which are intuitive, simple to
describe, and can yield qualitative results even when data is sparse.
We generate an expandable database of published, expert-curated Boolean GRN
models, and extracted the rules governing these networks. A meta-analysis of
this diverse set of models enables us to identify fundamental design principles
of GRNs.
The biological term canalization reflects a cell's ability to maintain a
stable phenotype despite ongoing environmental perturbations. Accordingly,
Boolean canalizing functions are functions where the output is already
determined if a specific variable takes on its canalizing input, regardless of
all other inputs. We provide a detailed analysis of the prevalence of
canalization and show that most rules describing the regulatory logic are
highly canalizing. Independent from this, we also find that most rules exhibit
a high level of redundancy. An analysis of the prevalence of small network
motifs, e.g. feed-forward loops or feedback loops, in the wiring diagram of the
identified models reveals several highly abundant types of motifs, as well as a
surprisingly high overabundance of negative regulations in complex feedback
loops. Lastly, we provide the strongest evidence thus far in favor of the
hypothesis that GRNs operate at the critical edge between order and chaos.Comment: 12 pages, 8 figure
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