1,410 research outputs found
Search for massive protostar candidates in the southern hemisphere: II. Dust continuum emission
In an ongoing effort to identify and study high-mass protostellar candidates
we have observed in various tracers a sample of 235 sources selected from the
IRAS Point Source Catalog, mostly with dec < -30 deg, with the SEST antenna at
millimeter wavelengths. The sample contains 142 Low sources and 93 High, which
are believed to be in different evolutionary stages. Both sub-samples have been
studied in detail by comparing their physical properties and morphologies.
Massive dust clumps have been detected in all but 8 regions, with usually more
than one clump per region. The dust emission shows a variety of complex
morphologies, sometimes with multiple clumps forming filaments or clusters. The
mean clump has a linear size of ~0.5 pc, a mass of ~320 Msolar for a dust
temperature Td=30 K, an H_2 density of 9.5E5 cm-3, and a surface density of 0.4
g cm-2. The median values are 0.4 pc, 102 Msolar, 4E4 cm-3, and 0.14 g cm-2,
respectively. The mean value of the luminosity-to-mass ratio, L/M ~99
Lsolar/Msolar, suggests that the sources are in a young, pre-ultracompact HII
phase. We have compared the millimeter continuum maps with images of the mid-IR
MSX emission, and have discovered 95 massive millimeter clumps non-MSX
emitters, either diffuse or point-like, that are potential prestellar or
precluster cores. The physical properties of these clumps are similar to those
of the others, apart from the mass that is ~3 times lower than for clumps with
MSX counterpart. Such a difference could be due to the potential prestellar
clumps having a lower dust temperature. The mass spectrum of the clumps with
masses above M ~100 Msolar is best fitted with a power-law dN/dM proportional
to M-alpha with alpha=2.1, consistent with the Salpeter (1955) stellar IMF,
with alpha=2.35.Comment: 83 pages, 10 figures, 3 tables. Accepted for publication by A&A. The
full paper, including Fig.2 with the maps of all the individual regions,
complete Tables 1 and 2 can be found at
http://www.arcetri.astro.it/~starform/publ2005.ht
BMP is an important regulator of proepicardial identity in the chick embryo
AbstractThe proepicardium (PE) is a transient structure formed by pericardial coelomic mesothelium at the venous pole of the embryonic heart and gives rise to several cell types of the mature heart. In order to study PE development in chick embryos, we have analyzed the expression pattern of the marker genes Tbx18, Wt1, and Cfc. During PE induction, the three marker genes displayed a left–right asymmetric expression pattern. In each case, expression on the right side was stronger than on the left side. The left–right asymmetric gene expression observed here is in accord with the asymmetric formation of the proepicardium in the chick embryo. While initially the marker genes were expressed in the primitive sinus horn, subsequently, expression became confined to the PE mesothelium. In order to search for signaling factors involved in PE development, we studied Bmp2 and Bmp4 expression. Bmp2 was bilaterally expressed in the sinus venosus. In contrast, Bmp4 expression was initially expressed unilaterally in the right sinus horn and subsequently in the PE. In order to assess its functional role, BMP signaling was experimentally modulated by supplying exogenous BMP2 and by inhibiting endogenous BMP signaling through the addition of Noggin. Both supplying BMP and blocking BMP signaling resulted in a loss of PE marker gene expression. Surprisingly, both experimental situations lead to cardiac myocyte formation in the PE cultures. Careful titration experiments with exogenously added BMP2 or Noggin revealed that PE-specific marker gene expression depends on a low level of BMP signaling. Implantation of BMP2-secreting cells or beads filled with Noggin protein into the right sinus horn of HH stage 11 embryos resulted in downregulation of Tbx18 expression, corresponding to the results of the explant assay. Thus, a distinct level of BMP signaling is required for PE formation in the chick embryo
Deterministic Fully Dynamic SSSP and More
We present the first non-trivial fully dynamic algorithm maintaining exact
single-source distances in unweighted graphs. This resolves an open problem
stated by Sankowski [COCOON 2005] and van den Brand and Nanongkai [FOCS 2019].
Previous fully dynamic single-source distances data structures were all
approximate, but so far, non-trivial dynamic algorithms for the exact setting
could only be ruled out for polynomially weighted graphs (Abboud and
Vassilevska Williams, [FOCS 2014]). The exact unweighted case remained the main
case for which neither a subquadratic dynamic algorithm nor a quadratic lower
bound was known.
Our dynamic algorithm works on directed graphs, is deterministic, and can
report a single-source shortest paths tree in subquadratic time as well. Thus
we also obtain the first deterministic fully dynamic data structure for
reachability (transitive closure) with subquadratic update and query time. This
answers an open problem of van den Brand, Nanongkai, and Saranurak [FOCS 2019].
Finally, using the same framework we obtain the first fully dynamic data
structure maintaining all-pairs -approximate distances within
non-trivial sub- worst-case update time while supporting optimal-time
approximate shortest path reporting at the same time. This data structure is
also deterministic and therefore implies the first known non-trivial
deterministic worst-case bound for recomputing the transitive closure of a
digraph.Comment: Extended abstract to appear in FOCS 202
Algorithm and Hardness for Dynamic Attention Maintenance in Large Language Models
Large language models (LLMs) have made fundamental changes in human life. The
attention scheme is one of the key components over all the LLMs, such as BERT,
GPT-1, Transformers, GPT-2, 3, 3.5 and 4. Inspired by previous theoretical
study of static version of the attention multiplication problem [Zandieh, Han,
Daliri, and Karbasi arXiv 2023, Alman and Song arXiv 2023]. In this work, we
formally define a dynamic version of attention matrix multiplication problem.
There are matrices , they represent query,
key and value in LLMs. In each iteration we update one entry in or . In
the query stage, we receive as input, and want to
answer , where is a square matrix and is a diagonal matrix. Here denote a length- vector
that all the entries are ones.
We provide two results: an algorithm and a conditional lower bound.
On one hand, inspired by the lazy update idea from [Demetrescu and
Italiano FOCS 2000, Sankowski FOCS 2004, Cohen, Lee and Song STOC 2019, Brand
SODA 2020], we provide a data-structure that uses
amortized update time, and
worst-case query time.
On the other hand, show that unless the hinted matrix vector
multiplication conjecture [Brand, Nanongkai and Saranurak FOCS 2019] is false,
there is no algorithm that can use both amortized update time, and worst query
time.
In conclusion, our algorithmic result is conditionally optimal unless hinted
matrix vector multiplication conjecture is false
Interrelation of ST-segment depression during bicycle ergometry and extent of myocardial ischaemia by myocardial perfusion SPECT
Purpose: The aim of this study was to compare ST-segment depression (STD) during bicycle ergometry and extent of myocardial ischaemia assessed by myocardial perfusion SPECT (MPS) in a large patient cohort. Methods: Consecutive patients (n = 955) referred for MPS with bicycle ergometry and interpretable stress ECG were evaluated with respect to ECG and MPS findings of ischaemia. The maximal STD was recorded and exercise ECG was considered ischaemic if STD was horizontal or downsloping (≥1mm). MPS was interpreted using a 20-segment model with a scale of 0 to 4. A summed stress (SSS), summed rest (SRS) and summed difference score (SDS = SSS−SRS, e.g. extent of ischaemia) were derived. Ischaemia was defined as an SDS ≥ 2. Results: An exercise-induced STD was present in 215 patients (22%) and myocardial ischaemia on MPS was present in 366 patients (38%). The extent of ST-segment depression and the number of ECG leads with significant STD were each strongly and significantly associated with increasing severity of ischaemia and the number of coronary territories involved (p < 0.01 for all correlations). Conclusion: These data demonstrate a strong correlation between the extent of STD, number of ischaemic leads and severity of myocardial ischaemia as assessed by MPS during bicycle ergometr
Flexible and stretchable electronics for wearable healthcare
Measuring the quality of human health and well-being is one of the key growth areas in our society. Preferably, these measurements are done as unobtrusive as possible. These sensoric devices are then to be integrated directly on the human body as a patch or integrated into garments. This requires the devices to be very thin, flexible and sometimes even stretchable. An overview will be given of recent technology developments in this domain and concrete application examples will be shown
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