Direct measurement of the nonconservative force field generated by optical tweezers

The force field of optical tweezers is commonly assumed to be conservative, neglecting the complex action of the scattering force. Using a novel method that extracts local forces from trajectories of an optically trapped particle, we measure the three dimensional force field experienced by a Rayleigh particle with 10 nm spatial resolution and femtonewton precision in force. We find that the force field is nonconservative with the nonconservative component increasing radially away from the optical axis, in agreement with the Gaussian beam model of the optical trap. Together with thermal position fluctuations of the trapped particle, the presence of the nonconservative force can cause a complex flux of energy into the optical trap depending on the experimental conditions

Development of a Fast Position-Sensitive Laser Beam Detector

We report the development of a fast position-sensitive laser beam detector with a bandwidth that exceeds currently available detectors. The detector uses a fiber-optic bundle that spatially splits the incident beam, followed by a fast balanced photo-detector. The detector is applied to the study of Brownian motion of particles on fast time scales with 1 Angstrom spatial resolution. Future applications include the study of molecule motors, protein folding, as well as cellular processes

PCPL: Predicate-Correlation Perception Learning for Unbiased Scene Graph Generation

Today, scene graph generation(SGG) task is largely limited in realistic scenarios, mainly due to the extremely long-tailed bias of predicate annotation distribution. Thus, tackling the class imbalance trouble of SGG is critical and challenging. In this paper, we first discover that when predicate labels have strong correlation with each other, prevalent re-balancing strategies(e.g., re-sampling and re-weighting) will give rise to either over-fitting the tail data(e.g., bench sitting on sidewalk rather than on), or still suffering the adverse effect from the original uneven distribution(e.g., aggregating varied parked on/standing on/sitting on into on). We argue the principal reason is that re-balancing strategies are sensitive to the frequencies of predicates yet blind to their relatedness, which may play a more important role to promote the learning of predicate features. Therefore, we propose a novel Predicate-Correlation Perception Learning(PCPL for short) scheme to adaptively seek out appropriate loss weights by directly perceiving and utilizing the correlation among predicate classes. Moreover, our PCPL framework is further equipped with a graph encoder module to better extract context features. Extensive experiments on the benchmark VG150 dataset show that the proposed PCPL performs markedly better on tail classes while well-preserving the performance on head ones, which significantly outperforms previous state-of-the-art methods.Comment: To be appeared on ACMMM 202

Analyzing The Impact Of Energy Efficient ASHRAE Guideline 36 Control Sequences On Demand Flexibility Potential Of Commercial Buildings: A Multi-Region Analysis

Traditional control sequences for HVAC systems in large commercial buildings have historically led to poor energy efficiency. To overcome this issue, ASHRAE has recently published Guideline 36 (G36), a collection of high-performance control sequences aimed at reducing energy consumption and cost for building owners. While these sequences are effective in increasing energy efficiency, their influence on a building's capacity to deliver demand flexibility remains uncertain. Prior research suggests a potential trade-off between energy efficiency and demand flexibility because permanently reducing energy use negatively impacts the available amount of load that can be reduced when responding to grid signals. To investigate this hypothesis, we created Modelica simulation models for an air handling unit with a G36 trim-and-respond sequence, calibrated these models to a fully instrumented experimental building testbed X1A in FLEXLAB, and simulated different demand flexibility scenarios. Counter to expectations, results show that, during a “shed event” with prior pre-cooling, G36 reduces demand by around 3.1 W/m2 more than the traditional control sequences, at the cost of a reduction in comfort (1.5 °C-hour/day) across five different cities across the United States. Our results provide encouraging evidence that, under the tested conditions, G36 does not decrease demand flexibility. This study should increase the confidence of building owners, designers, and operators who are looking to take advantage of demand flexibility programs while complying with increasingly stringent building energy efficiency standards

Transcriptionally active HERV-H retrotransposons demarcate topologically associating domains in human pluripotent stem cells.

Chromatin architecture has been implicated in cell type-specific gene regulatory programs, yet how chromatin remodels during development remains to be fully elucidated. Here, by interrogating chromatin reorganization during human pluripotent stem cell (hPSC) differentiation, we discover a role for the primate-specific endogenous retrotransposon human endogenous retrovirus subfamily H (HERV-H) in creating topologically associating domains (TADs) in hPSCs. Deleting these HERV-H elements eliminates their corresponding TAD boundaries and reduces the transcription of upstream genes, while de novo insertion of HERV-H elements can introduce new TAD boundaries. The ability of HERV-H to create TAD boundaries depends on high transcription, as transcriptional repression of HERV-H elements prevents the formation of boundaries. This ability is not limited to hPSCs, as these actively transcribed HERV-H elements and their corresponding TAD boundaries also appear in pluripotent stem cells from other hominids but not in more distantly related species lacking HERV-H elements. Overall, our results provide direct evidence for retrotransposons in actively shaping cell type- and species-specific chromatin architecture