Four decades since Mukaiyama’s first reports on the successful application of silicon and boron enolates in directed aldol reactions, the ability of this highly controlled carbon–carbon bond‐forming ...method to simultaneously define stereochemistry, introduce complexity, and construct the carbon skeleton with a characteristic 1,3‐oxygenation pattern has made it a powerful tool for natural product synthesis. This Minireview highlights a number of representative total syntheses that demonstrate the impact of the Mukaiyama aldol reaction and discusses the underlying mechanistic rationale that determines the stereochemical outcomes.
Four decades since Mukaiyama's first reports on the use of silicon and boron enolates in directed aldol reactions, this highly controlled carbon–carbon bond‐forming method has been developed into a powerful tool for natural product synthesis. A number of representative total syntheses that demonstrate the impact of the Mukaiyama aldol reaction are described and the underlying mechanistic rationale that determines the stereochemical outcomes is discussed.
Gravitational waves may be one of the few direct observables produced by ultralight bosons, conjectured dark matter candidates that could be the key to several problems in particle theory, ...high-energy physics and cosmology. These axionlike particles could spontaneously form "clouds" around astrophysical black holes, leading to potent emission of continuous gravitational waves that could be detected by instruments on the ground and in space. Although this scenario has been thoroughly studied, it has not been yet appreciated that both types of detector may be used in tandem (a practice known as "multibanding"). In this paper, we show that future gravitational-wave detectors on the ground and in space will be able to work together to detect ultralight bosons with masses 25 ≲ μ/(10−15 eV) ≲ 500. In detecting binary-black-hole inspirals, the LISA space mission will provide crucial information enabling future ground-based detectors, like Cosmic Explorer or Einstein Telescope, to search for signals from boson clouds around the individual black holes in the observed binaries. We lay out the detection strategy and, focusing on scalar bosons, chart the suitable parameter space. We study the impact of ignorance about the system's history, including cloud age and black hole spin. We also consider the tidal resonances that may destroy the boson cloud before its gravitational signal becomes detectable by a ground-based follow-up. Finally, we show how to take all of these factors into account, together with uncertainties in the LISA measurement, to obtain boson mass constraints from the ground-based observation facilitated by LISA.
Gravitational waves emitted by coalescing compact objects carry information about the spin of the individual bodies. However, with present detectors only the mass-weighted combination of the ...components of the spin along the orbital angular momentum can be measured accurately. This quantity, the effective spin ?eff, is conserved up to at least the second post-Newtonian order. The measured distribution of ?eff values from a population of detected binaries, and in particular whether this distribution is symmetric about zero, encodes valuable information about the underlying compact-binary formation channels. In this paper we focus on two important complications of using the effective spin to study astrophysical population properties: (i) an astrophysical distribution for ?eff values which is symmetric does not necessarily lead to a symmetric distribution for the detected effective spin values, leading to a selection bias; and (ii) the posterior distribution of ?eff for individual events is asymmetric and it cannot usually be treated as a Gaussian. We find that the posterior distributions for ?eff systematically show fatter tails toward larger positive values, unless the total mass is large or the mass ratio m2/m1 is smaller than ?1/2. Finally we show that uncertainties in the measurement of ?eff are systematically larger when the true value is negative than when it is positive. All these factors can bias astrophysical inference about the population when we have more than ?100 events and should be taken into account when using gravitational-wave measurements to characterize astrophysical populations.
Phase transitions share the universal feature of enhanced fluctuations near the transition point. Here, we show that density fluctuations reveal how a Bose-Einstein condensate of dipolar atoms ...spontaneously breaks its translation symmetry and enters the supersolid state of matter—a phase that combines superfluidity with crystalline order. We report on the first direct in situ measurement of density fluctuations across the superfluid-supersolid phase transition. This measurement allows us to introduce a general and straightforward way to extract the static structure factor, estimate the spectrum of elementary excitations, and image the dominant fluctuation patterns. We observe a strong response in the static structure factor and infer a distinct roton minimum in the dispersion relation. Furthermore, we show that the characteristic fluctuations correspond to elementary excitations such as the roton modes, which are theoretically predicted to be dominant at the quantum critical point, and that the supersolid state supports both superfluid as well as crystal phonons.
Background:
Cam-type femoroacetabular impingement (FAI) is a causative factor for hip pain and early hip osteoarthritis. Although cam FAI can alter hip joint biomechanics, it is unclear what role ...muscle forces play and how they affect the hip joint loading.
Purpose/Hypothesis:
The purpose was to examine the muscle contributions and hip contact forces in individuals with symptomatic cam FAI during level walking. Patients with symptomatic cam FAI would demonstrate different muscle and hip contact forces during gait.
Study Design:
Controlled laboratory study.
Methods:
Eighteen patients with symptomatic cam FAI were matched for age and body mass index with 18 control participants. Each participant’s walking kinematics and kinetics were recorded throughout a gait cycle (ipsilateral foot-strike to ipsilateral foot-off) by use of a motion capture system and force plates. Muscle and hip contact forces were subsequently computed by use of a musculoskeletal modeling program and static optimization methods.
Results:
The FAI group walked slower and with shorter steps, demonstrating reduced joint motions and moments during contralateral foot-strike, compared with the control group. The FAI group showed reduced psoas major (median, 1.1 newtons per bodyweight N/BW; interquartile range IQR, 1.0-1.5 N/BW) and iliacus forces (median, 1.2 N/BW; IQR, 1.0-1.6 N/BW), during contralateral foot-strike, compared with the control group (median, 1.6 N/BW; IQR, 1.3-1.6 N/BW, P = .004; and median, 1.5 N/BW; IQR, 1.3-1.6 N/BW, P = .03, respectively), which resulted in lower hip contact forces in the anterior (P = .026), superior (P = .02), and medial directions (P = .038). The 3 vectors produced a resultant peak force at the anterosuperior aspect of the acetabulum for both groups, with the FAI group demonstrating a substantially lower magnitude.
Conclusion:
FAI participants altered their walking kinematics and kinetics, especially during contralateral foot-strike, as a protective mechanism, which resulted in reduced psoas major and iliacus muscle force and anterosuperior hip contact force estimations.
Clinical Relevance:
Limited hip mobility not only is attributed to bone-on-bone impingement, caused by cam morphology, but could be attributed to musculature as well. Not only would the psoas major and iliacus be able to protect the hip joint during flexion-extension, athletic conditioning could further strengthen core muscles for improved hip mobility and pelvic balance.
Justice at the Millennium Colquitt, Jason A; Conlon, Donald E; Wesson, Michael J ...
Journal of applied psychology,
06/2001, Letnik:
86, Številka:
3
Journal Article
Recenzirano
The field of organizational justice continues to be marked by several important research questions, including the size of relationships among justice dimensions, the relative importance of different ...justice criteria, and the unique effects of justice dimensions on key outcomes. To address such questions, the authors conducted a meta-analytic review of 183 justice studies. The results suggest that although different justice dimensions are moderately to highly related, they contribute incremental variance explained in fairness perceptions. The results also illustrate the overall and unique relationships among distributive, procedural, interpersonal, and informational justice and several organizational outcomes (e.g., job satisfaction, organizational commitment, evaluation of authority, organizational citizenship behavior, withdrawal, performance). These findings are reviewed in terms of their implications for future research on organizational justice.
Summary
In this article, we study robust tensor completion by using transformed tensor singular value decomposition (SVD), which employs unitary transform matrices instead of discrete Fourier ...transform matrix that is used in the traditional tensor SVD. The main motivation is that a lower tubal rank tensor can be obtained by using other unitary transform matrices than that by using discrete Fourier transform matrix. This would be more effective for robust tensor completion. Experimental results for hyperspectral, video and face datasets have shown that the recovery performance for the robust tensor completion problem by using transformed tensor SVD is better in peak signal‐to‐noise ratio than that by using Fourier transform and other robust tensor completion methods.
Sphingolipids are a ubiquitous class of lipids present in a variety of organisms including eukaryotes and bacteria. In the last two decades, research has focused on characterizing the individual ...species of this complex family of lipids, which has led to a new field of research called 'sphingolipidomics'. There are at least 500 (and perhaps thousands of) different molecular species of sphingolipids in cells, and in Arabidopsis alone it has been reported that there are at least 168 different sphingolipids. Plant sphingolipids can be divided into four classes: glycosyl inositol phosphoceramides (GIPCs), glycosylceramides, ceramides, and free long-chain bases (LCBs). Numerous enzymes involved in plant sphingolipid metabolism have now been cloned and characterized, and, in general, there is broad conservation in the way in which sphingolipids are metabolized in animals, yeast and plants. Here, we review the diversity of sphingolipids reported in the literature, some of the recent advances in our understanding of sphingolipid metabolism in plants, and the physiological roles that sphingolipids and sphingolipid metabolites play in plant physiology.
Phthalocyanines and porphyrins are versatile functional pigments with a wide range of applications. These macrocyclic compounds contain four isoindole or pyrrole nitrogen atoms, which can complex ...with a range of metal ions. Large rare earth metal ions can bring together these tetrapyrrole derivatives to form sandwich-type double- and triple-decker complexes. Depending on the metal centers and the nature of the macrocyclic ligands, these compounds exhibit tunable spectroscopic, electronic, and redox properties, and different extents of intramolecular π−π interactions. Some of the properties of the sandwich-type complexes are unique and enable them to be used as advanced materials for various applications. Over the last two decades, a vast number of homoleptic and heteroleptic double- and triple-decker complexes have been synthesized. With improvements in synthetic procedures, researchers have prepared novel sandwich complexes that could not have been prepared by traditional methods. This Account highlights our work over the last decade on this important class of compounds. We have focused both on the development of facile and efficient synthetic methodology and on the various properties and potential applications of these complexes. For both the double- and triple-decker series, we have performed systematic investigations on several series of closely related analogues to reveal the correlations among the structures, electronic properties, spectroscopic characteristics, electrochemistry, and degree of π−π interactions. We have also performed detailed studies of the self-assembly of amphiphilic analogues in Langmuir−Blodgett films, metal-induced assembly of crown ether containing sandwich compounds, and the use of these complexes in organic field-effect transistors.
PDF
