Efficient Belief Road Map for Planning Under Uncertainty

Robotic systems, particularly in demanding environments like narrow corridors or disaster zones, often grapple with imperfect state estimation. Addressing this challenge requires a trajectory plan that not only navigates these restrictive spaces but also manages the inherent uncertainty of the system. We present a novel approach for graph-based belief space planning via the use of an efficient covariance control algorithm. By adaptively steering state statistics via output state feedback, we efficiently craft a belief roadmap characterized by nodes with controlled uncertainty and edges representing collision-free mean trajectories. The roadmap's structured design then paves the way for precise path searches that balance control costs and uncertainty considerations. Our numerical experiments affirm the efficacy and advantage of our method in different motion planning tasks. Our open-source implementation can be found at https://github.com/hzyu17/VIMP/tree/BRM

Positioning of self-assembled Ge islands on stripe-patterned Si (001) substrates

Self-assembled Ge islands were grown on stripe-patterned Si (001) substrates by solid source molecular beam epitaxy. The surface morphology obtained by atomic force microscopy (AFM) and cross-sectional transmission electron microscopy images (TEM) shows that the Ge islands are preferentially grown at the sidewalls of pure Si stripes along [-110] direction at 650o C or along the trenches, whereas most of the Ge islands are formed on the top terrace when the patterned stripes are covered by a strained GeSi buffer layer. Reducing the growth temperature to 600oC results in a nucleation of Ge islands both on the top terrace and at the sidewall of pure Si stripes. A qualitative analysis, based on the growth kinetics, demonstrates that the step structure of the stripes, the external strain field and the local critical wetting layer thickness for the islands formation contribute to the preferential positioning of Ge islands on the stripes.Comment: 10 pages, 7 figures, 1 table, the original paper is in print in J. Appl. Phy

Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures

The ability to control light-matter interaction is central to several potential applications in lasing, sensing, and communication. Graphene plasmons provide a way of strongly enhancing the interaction and realizing ultrathin optoelectronic devices. Here, we find that photoluminescence (PL) intensities of the graphene/GeSi quantum dots hybrid structures are saturated and quenched under positive and negative voltages at the excitation of 325 nm, respectively. A mechanism called plasmon-gating effect is proposed to reveal the PL dependence of the hybrid structures on the external electric field. On the contrary, the PL intensities at the excitation of 405 and 795 nm of the hybrid structures are quenched due to the charge transfer by tuning the Fermi level of graphene or the blocking of the excitons recombination by excitons separation effect. The results also provide an evidence for the charge transfer mechanism. The plasmon gating effect on the PL provides a new way to control the optical properties of graphene/QD hybrid structures

ID 144281)

We present a method to accurately measure the group birefringence variation with temperature in highbirefringence polarization-maintaining (PM) fibers using a distributed polarization analyzer. By analyzing polarization cross-talk peaks purposely induced at both ends of a PM fiber, the temperature coefficient of group birefringence can be accurately obtained. We confirm the theoretical prediction that the group birefringence of PANDA and TIGER PM fibers decrease linearly with temperature from −40°C to 80°C, and find that the temperature coefficients are −5:93 × 10 −7°C−1 and −5:29 × 10 −7°C−1 for two types of PANDA fibers, and −5:36 × 10 −7°C−1 for a TIGER fiber. © 2011 Optical Society of America OCIS codes: 060.2420, 260.1440, 260.2030, 060.2300.2370. The stress-induced birefringence, such as that in PANDA and TIGER polarization-maintaining (PM) fibers, is expected to be temperature dependent because it is caused by anisotropic strain resulting from the differential thermal expansion of different regions in the fiber cladding, and to vary linearly with temperature in the vicinity of room temperature [2], who measured the temperature dependence of the differential group delay of a PM fiber and obtained a linear temperature coefficient of −1:733 fs=°C · m (or −5:2 × 10 −7°C−1 ) from 625 to 1075 nm. The thermal coefficient of the group birefringence can be obtained by the accurate measurements of the group birefringence or beat length at different temperatures. Therefore, a good measurement setup must not only be able to measure the birefringence, but also allow the fiber under test to be placed in a temperature chamber without introducing significant measurement errors. The common methods for the beat length measurements of PM fibers include those of white-light spectral interferometry In this Letter, we report a new method of measuring the temperature variation of group birefringence of PM fibers using a distributed polarization cross-talk analyzer (General Photonics PXA-1000) and present the measurement results of three different PM fibers from three different manufacturers (PANDA-I, PANDA-II, and a TIGER PM fiber). The equipment can measure PM fibers with lengths up to 1:3 km and therefore allows a spool of PM fiber under test to be placed inside a temperature chamber with negligible error introduced. By linearfitting data to the theoretical formula using the least squares method, we confirm that the group birefringence in PM fibers of stress-induced birefringence, such as PANDA and TIGER fibers, decreases linearly with temperature. We show analytically that the major measurement error is inversely proportional to the fiber length and the method has an accuracy of less than 1.5% when fiber length is longer than 40 m. We find with high confidence that the temperature coefficients of group birefringence are −5:93 × 10 −7°C−1 , −5:29 × 10 −7°C−1 , and −5:36 × 10 −7°C−1 for PANDA-I, PANDA-II, and the TIGER fiber, respectively. PANDA and TIGER PM fibers belong to stress-induced birefringent fibers and their birefringence Δn b can be expressed by where T is the temperature of the fiber under test, T 0 is the softening temperature of the silica glass with dopants in the stress-inducing region of the cladding, and γ is the thermal coefficient of birefringence of the PM fiber, the parameter to be measured in this paper. The basic construction of a distributed polarization cross-talk analyze

Endoribonuclease YbeY Is Essential for RNA Processing and Virulence in Pseudomonas aeruginosa

Posttranscriptional regulation plays an essential role in the quick adaptation of pathogenic bacteria to host environments, and RNases play key roles in this process by modifying small RNAs and mRNAs. We find that the Pseudomonas aeruginosa endonuclease YbeY is required for rRNA processing and the bacterial virulence in a murine acute pneumonia model. Transcriptomic analyses reveal that knocking out the ybeY gene results in downregulation of oxidative stress response genes, including the catalase genes katA and katB Consistently, the ybeY mutant is more susceptible to H2O2 and neutrophil-mediated killing. Overexpression of katA restores the bacterial tolerance to H2O2 and neutrophil killing as well as virulence. We further find that the downregulation of the oxidative stress response genes is due to defective expression of the stationary-phase sigma factor RpoS. We demonstrate an autoregulatory mechanism of RpoS and find that ybeY mutation increases the level of a small RNA, ReaL, which directly represses the translation of rpoS through the 5' UTR of its mRNA and subsequently reduces the expression of the oxidative stress response genes. In vitro assays demonstrate direct degradation of ReaL by YbeY. Deletion of reaL or overexpression of rpoS in the ybeY mutant restores the bacterial tolerance to oxidative stress and the virulence. We also demonstrate that YbeZ binds to YbeY and is involved in the 16S rRNA processing and regulation of reaL and rpoS as well as the bacterial virulence. Overall, our results reveal pleiotropic roles of YbeY and the YbeY-mediated regulation of rpoS through ReaL.IMPORTANCE The increasing bacterial antibiotic resistance imposes a severe threat to human health. For the development of effective treatment and prevention strategies, it is critical to understand the mechanisms employed by bacteria to grow in the human body. Posttranscriptional regulation plays an important role in bacterial adaptation to environmental changes. RNases and small RNAs are key players in this regulation. In this study, we demonstrate critical roles of the RNase YbeY in the virulence of the pathogenic bacterium Pseudomonas aeruginosa We further identify the small RNA ReaL as the direct target of YbeY and elucidate the YbeY-regulated pathway on the expression of bacterial virulence factors. Our results shed light on the complex regulatory network of P. aeruginosa and indicate that inference with the YbeY-mediated regulatory pathway might be a valid strategy for the development of a novel treatment strategy.</p

The bracteatus pineapple genome and domestication of clonally propagated crops

Domestication of clonally propagated crops such as pineapple from South America was hypothesized to be a 'one-step operation'. We sequenced the genome of Ananas comosus var. bracteatus CB5 and assembled 513 Mb into 25 chromosomes with 29,412 genes. Comparison of the genomes of CB5, F153 and MD2 elucidated the genomic basis of fiber production, color formation, sugar accumulation and fruit maturation. We also resequenced 89 Ananas genomes. Cultivars 'Smooth Cayenne' and 'Queen' exhibited ancient and recent admixture, while 'Singapore Spanish' supported a one-step operation of domestication. We identified 25 selective sweeps, including a strong sweep containing a pair of tandemly duplicated bromelain inhibitors. Four candidate genes for self-incompatibility were linked in F153, but were not functional in self-compatible CB5. Our findings support the coexistence of sexual recombination and a one-step operation in the domestication of clonally propagated crops. This work guides the exploration of sexual and asexual domestication trajectories in other clonally propagated crops