Publications

CCDC 220099: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Improving the Quality of Health Care in the United Kingdom and the United States: A Framework for Change

Fueled by public incidents and growing evidence of deficiencies in care, concern over the quality and outcomes of care has increased in both the United Kingdom and the United States. Both countries have launched a number of initiatives to deal with these issues. These initiatives are unlikely to achieve their objectives without explicit consideration of the multilevel approach to change that includes the individual, group/team, organization, and larger environment/system level. Attention must be given to issues of leadership, culture, team development, and information technology at all levels. A number of contingent factors influence these efforts in both countries, which must each balance a number of tradeoffs between centralization and decentralization in efforts to sustain the impetus for quality improvement over time. The multilevel change framework and associated properties provide a framework for assessing progress along the journey.

xT: Nested Tokenization for Larger Context in Large Images

Modern computer vision pipelines handle large images in one of two sub-optimal ways: down-sampling or cropping. These two methods incur significant losses in the amount of information and context present in an image. There are many downstream applications in which global context matters as much as high frequency details, such as in real-world satellite imagery; in such cases researchers have to make the uncomfortable choice of which information to discard. We introduce xT, a simple framework for vision transformers which effectively aggregates global context with local details and can model large images end-to-end on contemporary GPUs. We select a set of benchmark datasets across classic vision tasks which accurately reflect a vision model's ability to understand truly large images and incorporate fine details over large scales and assess our method's improvement on them. xT is a streaming, two-stage architecture that adapts existing vision backbones and long sequence language models to effectively model large images without quadratic memory growth. We are able to increase accuracy by up to 8.6% on challenging classification tasks and $F_1$ score by 11.6 on context-dependent segmentation on images as large as 29,000 x 29,000 pixels.

Evaluation of Geostatistical Techniques for Reservoir Characterization

Abstract One of the most important problems in reservoir management and EOR applications is to describe interwell heterogeneity for optimum well spacing and process design. The conventional approaches to build reservoir descriptions use interpolation schemes based on the geometric distance of the samples. In geostatistics, on the other hand, the interpolated values depend on geometric orientation and correlation. Geostatistics has been used in the mining industry for the past forty years and in hydrogeology for the past twenty years. However, its application has been limited in reservoir engineering because of skepticism due to a lack of needed data and the absence of comparisons with the conventional techniques. Conventional and geostatistical reservoir characterization techniques are compared in this paper. Field data from about 50 wells are used in this evaluation. Interwell properties are computed using conventional and geostatistical techniques, cross-validated, and compared. Histograms show there are no geographically distinct populations requiring separate modeling. Experimental variograms identify the scales of variability of the reservoir properties and the existence of preferential directions of maximum and minimum variability. Variogram models are fitted to the experimental correlations. The results of this work indicate that the success of any technique is a function of the geological environment, selection of proper reservoir parameters for that environment, an adequate number of samples, an appropriate sample spacing, and most importantly, the correct application of the technique. Geostatistical techniques have more potential to incorporate the underlying correlation present in the data in the final analysis.

SLOW INVARIANT MANIFOLDS AS CURVATURE OF THE FLOW OF DYNAMICAL SYSTEMS

Considering trajectory curves, integral of n-dimensional dynamical systems, within the framework of Differential Geometry as curves in Euclidean n-space, it will be established in this article that the curvature of the flow, i.e. the curvature of the trajectory curves of any n-dimensional dynamical system directly provides its slow manifold analytical equation the invariance of which will be then proved according to Darboux theory. Thus, it will be stated that the flow curvature method, which uses neither eigenvectors nor asymptotic expansions but only involves time derivatives of the velocity vector field, constitutes a general method simplifying and improving the slow invariant manifold analytical equation determination of high-dimensional dynamical systems. Moreover, it will be shown that this method generalizes the Tangent Linear System Approximation and encompasses the so-called Geometric Singular Perturbation Theory. Then, slow invariant manifolds analytical equation of paradigmatic Chua's piecewise linear and cubic models of dimensions three, four and five will be provided as tutorial examples exemplifying this method as well as those of high-dimensional dynamical systems.

A Novel Semi-biosynthetic Route for Artemisinin Production Using Engineered Substrate-Promiscuous P450 _BM3

Production of fine chemicals from heterologous pathways in microbial hosts is frequently hindered by insufficient knowledge of the native metabolic pathway and its cognate enzymes; often the pathway is unresolved, and the enzymes lack detailed characterization. An alternative paradigm to using native pathways is de novo pathway design using well-characterized, substrate-promiscuous enzymes. We demonstrate this concept using P450(BM3) from Bacillus megaterium. Using a computer model, we illustrate how key P450(BM3) active site mutations enable binding of the non-native substrate amorphadiene. Incorporating these mutations into P450(BM3) enabled the selective oxidation of amorphadiene artemisinic-11S,12-epoxide, at titers of 250 mg L(-1) in E. coli. We also demonstrate high-yielding, selective transformations to dihydroartemisinic acid, the immediate precursor to the high-value antimalarial drug artemisinin.

Small-molecule biosensors for high-throughput metabolic engineering

Sleep disturbance and psychiatric disorders

Terrestrial Carbon Cycle Variability

<ns4:p>A growing literature is reporting on how the terrestrial carbon cycle is experiencing year-to-year variability because of climate anomalies and trends caused by global change. As CO<ns4:sub>2</ns4:sub> concentration records in the atmosphere exceed 50 years and as satellite records reach over 30 years in length, we are becoming better able to address carbon cycle variability and trends. Here we review how variable the carbon cycle is, how large the trends in its gross and net fluxes are, and how well the signal can be separated from noise. We explore mechanisms that explain year-to-year variability and trends by deconstructing the global carbon budget.</ns4:p><ns4:p> The CO<ns4:sub>2</ns4:sub> concentration record is detecting a significant increase in the seasonal amplitude between 1958 and now. Inferential methods provide a variety of explanations for this result, but a conclusive attribution remains elusive. Scientists have reported that this trend is a consequence of the greening of the biosphere, stronger northern latitude photosynthesis, more photosynthesis by semi-arid ecosystems, agriculture and the green revolution, tropical temperature anomalies, or increased winter respiration.</ns4:p><ns4:p> At the global scale, variability in the terrestrial carbon cycle can be due to changes in constituent fluxes, gross primary productivity, plant respiration and heterotrophic (microbial) respiration, and losses due to fire, land use change, soil erosion, or harvesting. It remains controversial whether or not there is a significant trend in global primary productivity (due to rising CO<ns4:sub>2</ns4:sub>, temperature, nitrogen deposition, changing land use, and preponderance of wet and dry regions). The degree to which year-to-year variability in temperature and precipitation anomalies affect global primary productivity also remains uncertain. For perspective, interannual variability in global gross primary productivity is relatively small (on the order of 2 Pg-C y<ns4:sup>-1</ns4:sup>) with respect to a large and uncertain background (123 +/- 4 Pg-C y<ns4:sup>-1</ns4:sup>), and detected trends in global primary productivity are even smaller (33 Tg-C y<ns4:sup>-2</ns4:sup>). Yet residual carbon balance methods infer that the terrestrial biosphere is experiencing a significant and growing carbon sink. Possible explanations for this large and growing net land sink include roles of land use change and greening of the land, regional enhancement of photosynthesis, and down regulation of plant and soil respiration with warming temperatures. Longer time series of variables needed to provide top-down and bottom-up assessments of the carbon cycle are needed to resolve these pressing and unresolved issues regarding how, why, and at what rates gross and net carbon fluxes are changing.</ns4:p>

Dynamically Chiral Expanded Helicenes

Expanded helicenes are a class of chiral nanographenes with a screw-shaped skeleton and a larger diameter than their classical ortho-fused counterparts. The flexibility of this internal cavity results in helicenes that are often difficult to isolate as single enantiomers. Expanded helicenes are therefore an intriguing target for exploration of dynamic chirality, a phenomenon resulting from introduction of chiral auxiliaries to control structure in a racemic system. This contribution describes installation of chiral amine substituents into the cavity of a diformyl expanded [11]-helicene by mild, efficient, and reversible imine condensations. The resulting helicenes display strong molar circular dichroism up to |Δε| = 300 M^-1 cm^-1 and absorption dissymmetry factors of |g_abs| = 0.010. The magnitude of circular dichroism can be varied by using different chiral amine substituents, which is correlated to the diastereomeric ratios of the helicenes. This is the first instance of dynamic chirality being used to observe a chiroptic response in expanded helicenes and is a significant synthetic improvement over methods which require conventional enantiomer resolution.

3D Spectroscopic View of Supernovae Using Light Echoes

CCDC 765494: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Posttraumatic stress reactions in volunteer firefighters

Abstract Volunteer firefighters in NSW were surveyed for experiences of posttraumatic stress. Firefighters were asked to describe their experiences of stress and indices were obtained of psychological disturbance. Findings indicated that most firefighters felt that their safety had been threatened. One‐quarter of firefighters indicated that they experienced significant levels of posttraumatic stress, although many respondents attributed their stress to personal events. Posttraumatic stress was associated with multiple and recent critical incidents. Findings are discussed in terms of etiological factors of posttraumatic stress and the need for appropriate intervention.

Reaktivität von Wolframocen gegenüber B‐B und B‐H‐Bindungen im Vergleich zu C‐H‐Bindungen

Bemerkenswert selektiv addiert photochemisch erzeugtes Wolframocen an die B‐B‐Bindung von Cat′BBCat′ (Cat′ = 4− t BuC 6 H 3 O 2 ) in Gegenwart von Benzol, was ein Gegensatz zur sonst üblichen Bevorzugung der Addition an C‐H‐Bindungen ist. Die leichte Spaltung von B‐B‐ und die bevorzugte Bildung von B‐H‐Bindungen kontrastieren mit den bei C‐C‐ und C‐H‐Aktivierungen bekannten Selektivitäten. Oben sind die Reaktionen von Wolframocen zusammengefaßt. magnified image

The Role of Determinism in the Prediction of Corrosion Damage

This paper explores the roles of empiricism and determinism in science and concludes that the intellectual exercise that we call “science” is best described as the transition from empiricism (i.e., observation) to determinism, which is the philosophy that the future can be predicted from the past based on the natural laws that are condensations of all previous scientific knowledge. This transition (i.e., “science”) is accomplished by formulating theories to explain the observations and models that are based on those theories to predict new phenomena. Thus, models are the computational arms of theories, and all models must possess a theoretical basis, but not all theories need to predict. The structure of a deterministic model is reviewed, and it is emphasized that all models must contain an input, a model engine, and an output, together with a feedback loop that permits the continual updating of the model parameters and a means of assessing predictions against new observations. This latter feature facilitates the application of the “scientific method” of cyclical prediction/assessment that continues until the model can no longer account for new observations. At that point, the model (and possibly the theory, too) has been “falsified” and must be discarded and a new theory/model constructed. In this regard, it is important to stress that no amount of successful prediction can prove a theory/model to be “correct”, because theories and models are merely the figments of our imagination as developed through imperfect senses and imperfect intellect and, hence, are invariably wrong at some level of detail. Contrariwise, a single failure of a model to predict an observation invalidates (“falsifies”) the theory/model. The impediment to model building is complexity and its impact on model building is discussed. Thus, we employ instruments such as microscopes and telescopes to extend our senses to examining smaller and larger objects, respectively, just as we now employ computers to extend our intellects as reflected in our computational prowess. The process of model building is illustrated with reference to the deterministic Coupled Environment Fracture Model (CEFM) that has proven to be highly successful in predicting crack growth rate in metals and alloys in contact with high-temperature aqueous environments of the type that exist in water-cooled nuclear power reactor primary coolant circuits.

CCDC 287138: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The effects of titania overlayers on C2H4/CO/H2 reactions over a Rh foil

Room-Temperature Coherent Optical Phonon in 2D Electronic Spectra of CH₃NH₃PbI₃ Perovskite as a Possible Cooling Bottleneck

A hot phonon bottleneck may be responsible for slow hot carrier cooling in methylammonium lead iodide hybrid perovskite, creating the potential for more efficient hot carrier photovoltaics. In room-temperature 2D electronic spectra near the band edge, we observe amplitude oscillations due to a remarkably long lived 0.9 THz coherent phonon population at room temperature. This phonon (or set of phonons) is assigned to angular distortions of the Pb-I lattice, not coupled to cation rotations. The strong coupling between the electronic transition and the 0.9 THz mode(s), together with relative isolation from other phonon modes, makes it likely to cause a phonon bottleneck. The pump frequency resolution of the 2D spectra also enables independent observation of photoinduced absorptions and bleaches independently and confirms that features due to band gap renormalization are longer-lived than in transient absorption spectra.