A 100-m-Scale Modeling Study of a Gale Event on the Lee Side of a Long Narrow Mountain

In this study, a gale event that occurred on the lee side of a long narrow mountain was investigated, together with the associated mountain flows, using a realistic-case large-eddy simulation (LES) that is based on the Weather Research and Forecasting Model. The mountain is located on the southeastern Tibetan Plateau, where approximately 58 gales occur annually, mostly in the afternoons during the winter season. Benefitting from realistic topography and high horizontal resolution as fine as 111 m, the LES can replicate features similar to the wind fields observed during the gale period. Investigation of the early morning wind structure over the mountain revealed that weak inflows were blocked, reversed, and divided in the upstream area and that some weak lee waves, rotors, and two clear lee vortices were evident downstream. As the upstream wind accelerated and the boundary layer developed during the daytime, the lee waves became amplified with severe downslope wind and rotors. The interaction and coherent structure of the downslope wind, rotor, and vortices were investigated to show the severe wind distribution. The mountain drags associated with blocking and amplified lee waves are displayed to show the potential impact on the large-scale model. The linear lee-wave theory was adopted to explain the wave evolution during this event together with a discussion of the uncertainty around low-level nonlinear processes

Molecular Packing Control Enables Excellent Performance and Mechanical Property of Blade-Cast All-Polymer Solar Cells

All-polymer solar cells (all-PSCs) are the most promising power generators for flexible and portable devices due to excellent morphology stability and outstanding mechanical property. Previous work indicates high crystallinity is beneficial to device performance but detrimental to mechanical property, therefore identifying the optimized ratio between crystalline and amorphous domains becomes important. In this work, we demonstrated highly efficient and mechanically robust all-PSCs by blade-coating technology in ambient environment based on PTzBI:N2200 system. By controlling the aggregation in solution state and ultrafast film formation process, a weakly ordered molecular packing morphology as well as small phase separation is obtained, which leads to not only the good photovoltaic performance (8.36%-one of the best blade-cast device in air) but also prominent mechanical characteristic. The controlled film shows a remarkable elongation with the crack onset strain of 15.6%, which is the highest result in organic solar cells without adding elastomers. These observations indicate the great promise of the developed all-PSCs for practical applications toward large-area processing technology

Effects of Molecular Structure and Packing Order on the Stretchability of Semicrystalline Conjugated Poly(Tetrathienoacene-diketopyrrolopyrrole) Polymers

The design of polymer semiconductors possessing high charge transport performance, coupled with good ductility, remains a challenge. Understanding the distribution and behavior of both crystalline domains and amorphous regions in conjugated polymer films, upon an applied stress, shall provide general guiding principles to design stretchable organic semiconductors. Structure–property relationships (especially in both side chain and backbone engineering) are investigated for a series of poly(tetrathienoacene-diketopyrrolopyrrole) polymers. It is observed that the fused thiophene diketopyrrolopyrrole-based polymer, when incorporated with branched side chains and an additional thiophene spacer in the backbone, exhibits improved mechanical endurance and, in addition, does not show crack propagation until 40% strain. Furthermore, this polymer exhibits a hole mobility of 0.1 cm2 V−1 s−1 even at 100% strain or after recovered from strain, which reveals prominent continuity and viscoelasticity of the polymer thin film. It is also observed that the molecular packing orientations (either edge-on or face-on) significantly affect the mechanical compliance of the polymer films. The improved stretchability of the polymers is attributed to both the presence of soft amorphous regions and the intrinsic packing arrangement of its crystalline domains

A multidimensional platform for the purification of non-coding RNA species

A renewed interest in non-coding RNA (ncRNA) has led to the discovery of novel RNA species and post-transcriptional ribonucleoside modifications, and an emerging appreciation for the role of ncRNA in RNA epigenetics. Although much can be learned by amplification-based analysis of ncRNA sequence and quantity, there is a significant need for direct analysis of RNA, which has led to numerous methods for purification of specific ncRNA molecules. However, no single method allows purification of the full range of cellular ncRNA species. To this end, we developed a multidimensional chromatographic platform to resolve, isolate and quantify all canonical ncRNAs in a single sample of cells or tissue, as well as novel ncRNA species. The applicability of the platform is demonstrated in analyses of ncRNA from bacteria, human cells and plasmodium-infected reticulocytes, as well as a viral RNA genome. Among the many potential applications of this platform are a system-level analysis of the dozens of modified ribonucleosides in ncRNA, characterization of novel long ncRNA species, enhanced detection of rare transcript variants and analysis of viral genomes.Singapore-MIT Alliance for Research and TechnologyNational Institute of Environmental Health Sciences (ES017010)National Institute of Environmental Health Sciences (ES002109

Evaluation of the Coupled WRF-Lake Model over the Great Lakes

A five-year simulation was performed using the advanced Research Weather Research and Forecasting (WRF) model version 3.2 coupled with a one-dimensional thermal diffusion lake scheme that has been enhanced with improved turbulent diffusion coefficients. In this study, the coupled WRF-Lake model is evaluated over the Great Lakes. The simulated monthly lake surface temperature (LST) and lake ice cover (LIC) during the winter months (December, January, and February) over the period of 2003 - 2007 are compared with MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data and output produced from WRF without a lake scheme. The results show that the coupled model is able to realistically simulate LST and LIC, and the spatial correlation coefficients between the WRF-Lake output and MODIS data are above 0.56 for the Great Lakes. The simulated biases from WRF-Lake for LST and LIC are significantly reduced as compared to those from WRF without a lake scheme. WRF-Lake also realistically reproduces the observed precipitation over the areas strongly affected by lake processes. The above results indicate that the coupled WRF-Lake model is very important to accurate predictions of weather and climate over lake-affected regions

Simulation of Thermal Structure in the Great Lakes using a Coupled WRF-Lake Model

A one-dimensional lake model has been successfully coupled to the Weather Research and Forecasting (WRF) model version 3.2 developed by the National Center for Atmospheric Research; the performance of the coupled model has been validated via simulations of physical processes in the Great Lakes. The results show that the coupled WRF-Iake model can realistically reproduce the thermal structure. in shallow waters (e.g., Lake Erie) while performing poorly in deep waters (e.g., Lake Superior). There are two main reasons that can explain why this lake model was unable to simulate the physical processes of deep waters. First, this lake model is one-dimensional, and many deep-lake physical phenomena that carry features of two or three dimensions cannot be described by a one-dimensional lake model. Second, the lake model uses a turbulent diffusion approach to parameterize the turbulent mixing in the lake, but such parameterization cannot generate sufficient turbulent mixing in the deep lake, which is essential to simulating water temperature profile and surface skin temperature. Through adjusting the eddy diffusivity in the lake model, the deep-lake temperature simulations are significantly improved when compared to observations. Such improvements will greatly benefit the research and prediction of regional weather, climate, and lake ecology

On the Roles of Advection and Solar Heating in Seasonal Variation of the Migrating Diurnal Tide in the Stratosphere, Mesosphere, and Lower Thermosphere

The migrating diurnal tide (DW1) presents a unique latitudinal structure in the stratosphere, mesosphere, and lower thermosphere. In this paper, the physical mechanisms that govern its seasonal variation are examined in these three regions using the 31.5-year (1979⁻2010) output from the extended Canadian Middle Atmosphere Model (eCMAM30). DW1 annual variation in the stratosphere is mainly controlled by the short-wave heating in the high latitudes, but by both the short-wave and adiabatic heating in the low latitudes. In the mesosphere, linear and nonlinear advection play important roles in the semiannual variation of the tide whereas short-wave heating does not. In the lower thermosphere, the annual variation of DW1 is mainly governed by the short-wave heating and linear advection. This study illustrates the complexity of the main physical mechanisms modulating the seasonal variations of DW1 in different regions of the atmosphere

High Performance Roll-To-Roll Printed PTB7-Th/PCBM Solar Cells (Conference Presentation)

Despite having surpassed 10% power conversion efficiency (PCE), widely held as the threshold for commercial viability, high performance organic photovoltaics (OPVs) are still mostly constrained to lab-scale devices fabricated by spin coating. Efforts to produce scalable printed OPVs trail significantly in efficiency, highlighting the need to better understand the processing-morphology-performance relationship in the context of linear printing processes. Here we investigate the OPV system PTB7-Th/PC71BM, which has demonstrated \u3e10% PCE via spincoating but only exhibits ~1% PCE when roll-to-roll printed. Of particular interest is the ubiquitous alcohol wash post-treatment applied to the dried active layer, which induces a significant improvement in device performance, and its crucial role for printed films. While it has been speculated that the primary utility of the alcohol post-treatment is to remove the additive 1,8-diiodooctane (DIO) residue in the dried film, we find here that the wash process itself dramatically impacts morphology in printed films regardless of the presence of DIO. Here we employ various x-ray characterization techniques to probe phase separation, crystallinity, and molecular orientation, as well as in-situ grazing-incidence x-ray diffraction (in-situ GIXD) to monitor morphological evolution during the isopropanol post-treatment process. It is discovered that isopropanol induces significant donor polymer alignment and enhanced π-π degree of crystallinity. Through the understanding gained in this study, we are able to achieve a roll-to-roll printed OPV with 5% PCE, which is to our knowledge the highest reported performance for a roll-to-roll printed single junction photoactive layer on a flexible substrate