Spatiotemporal Uniformity Research Articles

Ultrathin quasi-2D amorphous carbon dielectric prepared from solution precursor for nanoelectronics

Materials keeping thickness in atomic scale but extending primarily in lateral dimensions offer properties attractive for many emerging applications. However, compared to crystalline counterparts, synthesis of atomically thin films in the highly disordered amorphous form, which avoids nonuniformity and defects associated with grain boundaries, is challenging due to their metastable nature. Here we present a scalable and solution-based strategy to prepare large-area, freestanding quasi-2D amorphous carbon nanomembranes with predominant sp2 bonding and thickness down to 1–2 atomic layers, from coal-derived carbon dots as precursors. These atomically thin amorphous carbon films are mechanically strong with modulus of 400 ± 100 GPa and demonstrate robust dielectric properties with high dielectric strength above 20 MV cm−1 and low leakage current density below 10−4 A cm−2 through a scaled thickness of three-atomic layers. They can be implemented as solution-deposited ultrathin gate dielectrics in transistors or ion-transport media in memristors, enabling exceptional device performance and spatiotemporal uniformity.

Transport and Reaction Modeling of Nanocarriers for Cancer Therapeutics: Experimental and in silico approaches

Reaction-diffusion mathematical modeling plays a fundamental role in understanding and optimizing the performance of heterogeneous catalysts. The successful exploitation of all catalyst sites in these porous heterogeneous materials bears a striking analogy -conceptually and mathematically- with successfully delivering drugs throughout avascular regions of solid tumors: the drugs need to ``react with” and kill (almost) all of the constituent cancer cells. We use reaction-diffusion modeling to describe non-intuitive cocktails of engineered biomaterials –with diverse drug delivery properties– with the goal of identifying 'geographically complementary' behaviors of transport, reaction, and cell kill. The aim is to “leave no cancer cell behind”. We have experimentally demonstrated in mouse models that effectively killing solid tumors does not require cocktails of different drugs. It is the spatiotemporal uniformity of the delivered drug that is important, rather than a variety of drugs, or the total drug delivered per mass of the tumor. No single delivery carrier possesses the plethora of diverse properties needed to enable uniform and prolonged delivery of therapeutics within the entire volume of the avascular regions of solid tumors. We, therefore, use combinations of different delivery carriers of the same drug – carriers with complementary properties, enabled by the mathematical modeling predictions.

Growth Inhibition of Triple-Negative Breast Cancer: The Role of Spatiotemporal Delivery of Neoadjuvant Doxorubicin and Cisplatin.

Combinations of platinum-based compounds with doxorubicin in free and/or in liposomal form for improved safety are currently being evaluated in the neoadjuvant setting on patients with advanced triple-negative breast cancer (TNBC). However, TNBC may likely be driven by chemotherapy-resistant cells. Additionally, established TNBC tumors may also exhibit diffusion-limited transport, resulting in heterogeneous intratumoral delivery of the administered therapeutics; this limits therapeutic efficacy in vivo. We studied TNBC cells with variable chemosensitivities, in the absence (on monolayers) and presence (in 3D multicellular spheroids) of transport barriers; we compared the combined killing effect of free doxorubicin and free cisplatin to the killing effect (1) of conventional liposomal forms of the two chemotherapeutics, and (2) of tumor-responsive lipid nanoparticles (NP), specifically engineered to result in more uniform spatiotemporal microdistributions of the agents within solid tumors. This was enabled by the NP properties of interstitial release, cell binding/internalization, and/or adhesion to the tumors’ extracellular matrix. The synergistic cell kill by combinations of the agents (in all forms), compared to the killing effect of each agent alone, was validated on monolayers of cells. Especially for spheroids formed by cells exhibiting resistance to doxorubicin combination treatments with both agents in free and/or in tumor-responsive NP-forms were comparably effective; we not only observed greater inhibition of outgrowth compared to the single agent(s) but also compared to the conventional liposome forms of the combined agents. We correlated this finding to more uniform spatiotemporal microdistributions of agents by the tumor-responsive NP. Our study shows that combinations of NP with properties specifically optimized to improve the spatiotemporal uniformity of the delivery of their corresponding therapeutic cargo can improve treatment efficacy while keeping favorable safety profiles.

Hydrochemistry and heavy metals concentrations in sediment of Woji creek and Bonny estuary, Niger Delta, Nigeria

Physicochemical characteristics of the surface water and heavy metals levels in sediment of Woji creek and upper reaches of the Bonny estuary, Niger Delta, Nigeria were investigated between October, 2012 and September, 2014. Ten sampling stations were established along the main creek course based on accessibility and proximity gradient from expected pollution sources. Water and sediment samples were collected monthly at each sampling station for twenty four months, using Hydrobios Water Sampler and Van-veen grab respectively. Water samples were analysed in the laboratory following standard procedures. Heavy metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd and Pb) levels in sediment were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The surface water temperature showed seasonal changes, pH (6.68 ± 0.7) showed spatio-temporal uniformity throughout the study period and Total Organic Carbon (TOC) was generally low (0.23 ± 0.06). There was no seasonal variation in Biochemical oxygen demand (BOD5). Salinity showed a positive correlation with pH and conductivity but negative correlation with temperature. Physicochemical properties of the water body were however, within Federal Ministry of Environment set limits for coastal water. The levels of heavy metals in sediments were in the order: Fe > Mn > Cu > Ni > Co > Zn > As > Cr > Pb > Cd. Sediments were found to have low levels enrichment of heavy metals from anthropogenic sources. This could be as a result of high tidal flushing in the study area. Pollution load index (PLI) and the degree of contamination (Cd) evaluated showed that sediment of the study area has low level of contamination from heavy metals and can be said to be relatively unpolluted.

Spatiotemporal propagation dynamics of intense optical pulses in loosely confined gas-filled hollow-core fibers

We numerically study the propagation dynamics of intense optical pulses in gas-filled hollow-core fibers (HCFs). The spatiotemporal dynamics of the pulses show a transition from tightly confined to loosely confined characteristics as the fiber core is increased, which manifests as a deterioration in the spatiotemporal uniformity of the beam. It is found that using the gas pressure gradient does not enhance the beam quality in large-core HCFs, while inducing a positive chirp in the pulse to lower the peak power can improve the beam quality. This indicates that the self-focusing effect in the HCFs is the main driving force for the propagation dynamics. It also suggests that pulses at longer wavelengths are more suitable for HCFs with large cores because of the lower critical power of self-focusing, which is justified by the numerical simulations. These results will benefit the generation of energetic few-cycle pulses in large-core HCFs.

Rapid short-pulse sequences enhance the spatiotemporal uniformity of acoustically driven microbubble activity during flow conditions.

Despite the promise of microbubble-mediated focused ultrasound therapies, in vivo findings have revealed over-treated and under-treated regions distributed throughout the focal volume. This poor distribution cannot be improved by conventional pulse shapes and sequences, due to their limited ability to control acoustic cavitation dynamics within the ultrasonic focus. This paper describes the design of a rapid short-pulse (RaSP) sequence which is comprised of short pulses separated by μs off-time intervals. Improved acoustic cavitation distribution was based on the hypothesis that microbubbles can freely move during the pulse off-times. Flowing SonoVue® microbubbles (flow velocity: 10 mm/s) were sonicated with a 0.5 MHz focused ultrasound transducer using RaSP sequences (peak-rarefactional pressures: 146-900 kPa, pulse repetition frequency: 1.25 kHz, and pulse lengths: 5-50 cycles). The distribution of cavitation activity was evaluated using passive acoustic mapping. RaSP sequences generated uniform distributions within the focus in contrast to long pulses (50 000 cycles) that produced non-uniform distributions. Fast microbubble destruction occurred for long pulses, whereas microbubble activity was sustained for longer durations for shorter pulses. High-speed microscopy revealed increased mobility in the direction of flow during RaSP sonication. In conclusion, RaSP sequences produced spatiotemporally uniform cavitation distributions and could result in efficient therapies by spreading cavitation throughout the treatment area.

LIBSVX: A Supervoxel Library and Benchmark for Early Video Processing

Supervoxel segmentation has strong potential to be incorporated into early video analysis as superpixel segmentation has in image analysis. However, there are many plausible supervoxel methods and little understanding as to when and where each is most appropriate. Indeed, we are not aware of a single comparative study on supervoxel segmentation. To that end, we study seven supervoxel algorithms, including both off-line and streaming methods, in the context of what we consider to be a good supervoxel: namely, spatiotemporal uniformity, object/region boundary detection, region compression and parsimony. For the evaluation we propose a comprehensive suite of seven quality metrics to measure these desirable supervoxel characteristics. In addition, we evaluate the methods in a supervoxel classification task as a proxy for subsequent high-level uses of the supervoxels in video analysis. We use six existing benchmark video datasets with a variety of content-types and dense human annotations. Our findings have led us to conclusive evidence that the hierarchical graph-based (GBH), segmentation by weighted aggregation (SWA) and temporal superpixels (TSP) methods are the top-performers among the seven methods. They all perform well in terms of segmentation accuracy, but vary in regard to the other desiderata: GBH captures object boundaries best; SWA has the best potential for region compression; and TSP achieves the best undersegmentation error.

Spatial heterogeneity of ecosystem health and its sensitivity to pressure in the waters of nearshore archipelago

The ecosystem-based management of nearshore waters requires synthesis of spatial data on the distribution of ecological conditions and intensity of anthropogenic perturbations, and the overlay of their effects on the ecosystem health. An assessment framework for ecosystem health incorporating 4 components namely vigor, organization, resilience and maintenance was proposed in this paper, based on which an analytical approach was developed to quantify the integrated effects of island mass and anthropogenic pressures on the waters of nearshore archipelago. The southern waters of Miaodao Archipelago, which are located in the intersection of the Bohai Sea and the Yellow Sea, China, were taken as a typical example to acquire the spatial heterogeneity of the ecosystem health and its sensitivity to multiple anthropogenic pressures. Results indicated that there was a relatively significant performance of the spatial heterogeneity for the ecosystem health. It presented that the interisland waters were poorer health than the external waters, and the waters adjacent to the continent functioned less well than those in a relatively open area. This phenomenon was primarily determined by the performance of vigor as well as resilience of ecosystem. For the 4 components of ecosystem health, there were an obvious spatial heterogeneity of vigor as well as the resilience, a seasonal succession of organization, and a spatiotemporal uniformity of maintenance. Moreover, the ecosystem health was more sensitive to the stressors of inland activities and coastline exploitation especially in the waters of Miaodao Bay and Changdao Port. The analytical process and resulting maps provide flexible tools for regional efforts to implement ecosystem-based management in the waters of archipelago and further nearshore waters so as to promote their sustainable development.

Soil–landscape response to mid and late Quaternary climate fluctuations based on numerical simulations

We use a numerical dynamic soil–landscape model to study one aspect of the spatio-temporal soil–landscape evolution process, the effect of climatic fluctuations on soil grading distribution in space and time in response to the interplay between physical weathering and surface erosion (soil mineralogical fluxes). We simulate a synthetic soil–landscape system over the middle and late Quaternary (last 400ka). The results show that (1) soil–landscape response to climate change is non-linear and highly spatially variable, even at hillslope scale; and (2) soil–landscape adjustment to climate change can lag tens of thousands of years and is both spatially and temporally variable. We propose that the legacy of past climatic condition (i.e. last glacial maximum) in modern soil–landscape systems vary considerably in space. This implies that the spatiotemporal uniformity in which soil is typically described in Earth system modeling and analysis (e.g. carbon cycle) grossly underestimates their actual complexity.

Global Modernity and Temporal Multiplicity

AbstractGlobal modernity is not only shrinking the world in terms of communication, trade, travel and many forms of social exchange but also implanting the idea that only the present matters. This logic of ‘presentism’ is infused with a growing sense of sameness precipitated by the rapidity of transnational commercialism and the seductive pull of neo-liberal ideologies. In a context marked by a hypermodern inflation of wants and commodities, the notion of globality cannot do without a perspective that emphasizes the spatialization of time where distance becomes almost superfluous. Yet the shrinking of the world is not exclusively space-centered since concurrent exposure to myriad cultures and their histories is producing an alternate sensitivity to time-centered meanings of modernity. By historicizing change, temporal geographies emerge in the form of multiple modernities that makes problematic the idea of spatio-temporal uniformity in a globalized world. Instead, crosscurrents of global interconnectivity are producing varying patterns of spatial and temporal perception to suggest a new sense of co-evalness or an interplay of diachronic, synchronic and desynchronized actions.

Simple linear technique for the measurement of space–time coupling in ultrashort optical pulses

We demonstrate a simple sensitive linear technique that quantifies the spatiotemporal coupling in the electric field of an ultrashort optical pulse. The space-time uniformity of the field can be determined with only time-stationary filters and square-law integrating detectors, even if it is impossible to measure the temporal electric field in this way. A degree of spatiotemporal uniformity is defined and can be used with the demonstrated diagnostic to quantify space-time coupling. Experimental measurements of space-time coupling due to linear and nonlinear focusing, refraction, and diffraction are presented.

Facilitation of intracellular H(+) ion mobility by CO(2)/HCO(3)(-) in rabbit ventricular myocytes is regulated by carbonic anhydrase.

Intracellular H(+) mobility was estimated in the rabbit isolated ventricular myocyte by diffusing HCl into the cell from a patch pipette, while imaging pH(i) confocally using intracellular ratiometric SNARF fluorescence. The delay for acid diffusion between two downstream regions approximately 40 microm apart was reduced from approximately 25 s to approximately 6 s by replacing Hepes buffer in the extracellular superfusate with a 5 % CO(2)/HCO(3)(-) buffer system (at constant pH(o) of 7.40). Thus CO(2)/HCO(3)(-) (carbonic) buffer facilitates apparent H(+)(i) mobility. The delay with carbonic buffer was increased again by adding acetazolamide (ATZ), a membrane permeant carbonic anhydrase (CA) inhibitor. Thus facilitation of apparent H(+)(i) mobility by CO(2)/HCO(3)(-) relies on the activity of intracellular CA. By using a mathematical model of diffusion, the apparent intracellular H(+) equivalent diffusion coefficient (D(H)(app)) in CO(2)/HCO(3)(-)-buffered conditions was estimated to be 21.9 x 10(-7) cm(2) s(-1), 5.8 times faster than in the absence of carbonic buffer. Facilitation of H(+)(i) mobility is discussed in terms of an intracellular carbonic buffer shuttle, catalysed by intracellular CA. Turnover of this shuttle is postulated to be faster than that of the intrinsic buffer shuttle. By regulating the carbonic shuttle, CA regulates effective H(+)(i) mobility which, in turn, regulates the spatiotemporal uniformity of pH(i). This is postulated to be a major function of CA in heart.