1,798 research outputs found
Total Synthesis of Mycinolide IV and Path‐Scouting for Aldgamycin N
Proof‐of‐concept is provided that a large estate of 16‐membered macrolide antibiotics can be reached by a “unified” approach. The key building block was formed on scale by an asymmetric vinylogous Mukaiyama aldol reaction; its alkene terminus was then converted either into the corresponding methyl ketone by Wacker oxidation or into a chain‐extended aldehyde by catalyst‐controlled branch‐selective asymmetric hydroformylation. These transformations ultimately opened access to two structurally distinct series of macrolide targets. Notable late‐stage maneuvers comprise a rare example of a ruthenium‐catalyzed redox isomerization of an 1,3‐enyne‐5‐ol into a 1,3‐diene‐5‐one derivative, as well as the elaboration of a tertiary propargylic alcohol into an acyloin by trans‐hydrostannation/Chan‐Lam‐type coupling. Moreover, this case study illustrates the underutilized possibility of forging complex macrolactone rings by transesterification under essentially neutral conditions
CID: Chemistry In Disks VII. First detection of HC3N in protoplanetary disks
Molecular line emission from protoplanetary disks is a powerful tool to
constrain their physical and chemical structure. Nevertheless, only a few
molecules have been detected in disks so far. We take advantage of the enhanced
capabilities of the IRAM 30m telescope by using the new broad band correlator
(FTS) to search for so far undetected molecules in the protoplanetary disks
surrounding the TTauri stars DM Tau, GO Tau, LkCa 15 and the Herbig Ae star MWC
480. We report the first detection of HC3N at 5 sigma in the GO Tau and MWC 480
disks with the IRAM 30-m, and in the LkCa 15 disk (5 sigma), using the IRAM
array, with derived column densities of the order of 10^{12}cm^{-2}. We also
obtain stringent upper limits on CCS (N < 1.5 x 10^{12} cm^{-3}). We discuss
the observational results by comparing them to column densities derived from
existing chemical disk models (computed using the chemical code Nautilus) and
based on previous nitrogen and sulfur-bearing molecule observations. The
observed column densities of HC3N are typically two orders of magnitude lower
than the existing predictions and appear to be lower in the presence of strong
UV flux, suggesting that the molecular chemistry is sensitive to the UV
penetration through the disk. The CCS upper limits reinforce our model with low
elemental abundance of sulfur derived from other sulfur-bearing molecules (CS,
H2S and SO).Comment: 8 pages, 4 figures, 3 tables, Accepted for publication in Ap
Federated Continual Learning to Detect Accounting Anomalies in Financial Auditing
The International Standards on Auditing require auditors to collect
reasonable assurance that financial statements are free of material
misstatement. At the same time, a central objective of Continuous Assurance is
the real-time assessment of digital accounting journal entries. Recently,
driven by the advances in artificial intelligence, Deep Learning techniques
have emerged in financial auditing to examine vast quantities of accounting
data. However, learning highly adaptive audit models in decentralised and
dynamic settings remains challenging. It requires the study of data
distribution shifts over multiple clients and time periods. In this work, we
propose a Federated Continual Learning framework enabling auditors to learn
audit models from decentral clients continuously. We evaluate the framework's
ability to detect accounting anomalies in common scenarios of organizational
activity. Our empirical results, using real-world datasets and combined
federated continual learning strategies, demonstrate the learned model's
ability to detect anomalies in audit settings of data distribution shifts.Comment: 6 pages (excl. appendix), 5 figures, 1 table, preprint version,
currently under revie
Tool Capabilities needed for Designing 100 MHz Interconnects
Abstract -Printed circuit board design complexity increases greatly as bus speeds exceed 100 MHz. This increased complexity is due more to the large number of simulations a designer must complete rather than simulation or modeling accuracy. This paper presents the case for these increased numbers of simulations, and presents techniques for managing this complexity
Reorientation of Spin Density Waves in Cr(001) Films induced by Fe(001) Cap Layers
Proximity effects of 20 \AA thin Fe layers on the spin density waves (SDWs)
in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk
Cr we observe a SDW with its wave vector Q pointing along only one {100}
direction which depends dramatically on the film thickness t_{Cr}. For t_{Cr} <
250 \AA the SDW propagates out-of-plane with the spins in the film plane. For
t_{Cr} > 1000 \AA the SDW propagates in the film plane with the spins
out-of-plane perpendicular to the in-plane Fe moments. This reorientation
transition is explained by frustration effects in the antiferromagnetic
interaction between Fe and Cr across the Fe/Cr interface due to steps at the
interface.Comment: 4 pages (RevTeX), 3 figures (EPS
Causal effects of an absent crowd on performances and refereeing decisions during Covid-19
The Covid-19 pandemic has induced worldwide natural experiments on the effects of crowds. We exploit one of these experiments that took place over several countries in almost identical settings: professional football matches played behind closed doors within the 2019/20 league seasons. We find large and statistically significant effects on the number of yellow cards issued by referees. Without a crowd, fewer cards were awarded to the away teams, reducing home advantage. These results have implications for the influence of social pressure and crowds on the neutrality of decisions
Syzygies of torsion bundles and the geometry of the level l modular variety over M_g
We formulate, and in some cases prove, three statements concerning the purity
or, more generally the naturality of the resolution of various rings one can
attach to a generic curve of genus g and a torsion point of order l in its
Jacobian. These statements can be viewed an analogues of Green's Conjecture and
we verify them computationally for bounded genus. We then compute the
cohomology class of the corresponding non-vanishing locus in the moduli space
R_{g,l} of twisted level l curves of genus g and use this to derive results
about the birational geometry of R_{g, l}. For instance, we prove that R_{g,3}
is a variety of general type when g>11 and the Kodaira dimension of R_{11,3} is
greater than or equal to 19. In the last section we explain probabilistically
the unexpected failure of the Prym-Green conjecture in genus 8 and level 2.Comment: 35 pages, appeared in Invent Math. We correct an inaccuracy in the
statement of Prop 2.
A rotating molecular jet from a Perseus protostar
We present CO(2-1) line and 1.4 mm continuum archival observations,
made with the Submillimeter Array, of the outflow HH 797 located in the IC 348
cluster in Perseus. The continuum emission is associated with a circumstellar
disk surrounding the class 0 object IC 348-MMS/SMM2, a very young solar analog.
The line emission, on the other hand, delineates a collimated outflow, and
reveals velocity asymmetries about the flow axis over the entire length of the
flow. The amplitude of velocity differences is of order 2 km s over
distances of about 1000 AU, and we interpret them as evidence for jet rotation
--although we also discuss alternative possibilities. A comparison with
theoretical models suggests that the magnetic field lines threading the
protostellar jet might be anchored to the disk of a radius of about 20 AU.Comment: Accepted for publication in Ap
Prerequisites for setting up management system in municipal retail trade
The relevance of the problem is determined by the number of complex problems that exist in present Samara municipal retail trade system, which is manifested in the lack of regulation, a glut of sales area, poorly developed infrastructure. The purpose of this article is to form a quantitative base for determining the municipal needs in the floor space. Leading method to study this problem is the method of empirical observations and mathematical modeling. The study results: the article contains the analysis of sales area availability on the example in the urban district and presents a quantitative method to determine predictive values for retail trade turnover. Practical significance: the paper is aimed to develop managerial decisions in the sphere of municipal trade regulation. © 2016 Suraeva et al
- …