889 research outputs found
Methodologies to Predict Service Lives of Pavement Marking Materials
This study focuses on developing methodologies to predict the service life of a pavement marking material based on its retroreflectivity. Data from the 2002 National Transportation Product Evaluation Program (NTPEP) pavement marking material test deck in Mississippi are used for model development and model validation. The smoothing spline method and time series modeling are applied to estimate the service lives of different types of materials based on the assumption of a required minimum retroreflectivity value. The same models can also predict the retroreflectivity values at future times for a pavement marking product based on its retroreflectivity values in the past. The validation of the models shows satisfactory accuracy. As demonstrated in a case study, the predicted service lives of the marking materials can be used in life-cycle cost comparisons for selecting pavement marking material
Degenerate lower dimensional tori in reversible systems
AbstractIn this paper we prove the persistence of lower dimensional invariant tori with prescribed frequencies and singular normal matrices in reversible systems. The normal variable is two-dimensional and the unperturbed nonlinear terms in the differential equation for this variable have a special structure
A nano-tensile testing system for studying nanostructures inside an electron microscope:design, characterization and application
Mechanical properties of nanostructures could be remarkably different from their bulk counterparts owing to scale effects, which have attracted considerable research interest in recent years. However, nanomechanics studies are hindered by the difficulties of conducting well-instrumented mechanical testing. The objective of this thesis is to develop a novel tensile stage that can be used to probe mechanical properties of universal one-dimensional (1D) nanostructures, like nanowires and nanotubes, inside a scanning/transmission electron microscope (SEM/TEM). The main challenges of performing tensile tests at the nanoscale are: (1) specimen alignment and fixation on the tensile stage; (2) application and measurement of tensile force with nano-Newton resolution; (3) measurement of specimen elongation with nanometer resolution. Previous studies have shown that micro-electromechanical system (MEMS) technology combined with advanced microscopy (e.g. SEM and TEM) provides promising perspectives to address these challenges. Two types of nano-tensile stages, fabricated in a silicon on insulator (SOI) wafer, were developed in this thesis, which consisted of a comb-drive actuator and either a differential capacitive force sensor or a double clamped beam force sensor. The optimized comb-drive actuators could output an in-plane force of about 210 µN at a drive voltage of 120 V, and the force sensors achieved resolutions of better than 50 nN. Individual 1D nanostructures were placed on the MEMS device by in-situ nanomanipulations and fixed at their two ends via focused electron beam induced deposition (FEBID). A strategy of modifying device topography, e.g. in the form of trenches or pillars, was proposed to facilitate the specimen preparation by in-situ manipulation that could achieve a high yield of about 80%. The mechanical testing function of the developed micro devices was demonstrated by tensile tests on individual Co and Si nanowires (NWs) inside an SEM. The average apparent Young's modulus, tensile strength and fracture strain of the electrochemically deposited Co NWs were measured to be (75.3±14.6) GPa, (1.6±0.4) GPa and (2.2±0.6) %, respectively. The measured Young's modulus is significantly lower than that of Co in the bulk form (209 GPa), which is likely caused by structural defects (e.g. pores) and surface effects (e.g. surface contaminations and surface oxide layers). The phosphorous-doped SiNWs grown bottom up by the vapor-liquid-solid (VLS) technique showed an average Young's modulus of (170.0±2.4) GPa and a tensile strength larger than 8.3 GPa. This finding confirms that materials strength increases as their sizes scale down. The top down electroless chemically etched Si NWs show a tensile strength of 5.4 GPa. The developed MEMS devices and experimental techniques enable an alternative way of in-situ nanomechanical characterization based on electron microscopy. The design methodology and learning presented in this thesis would be useful to develop nano-tensile stages of other configurations with more advanced functions
Social-Mobility-Aware Joint Communication and Computation Resource Management in NOMA-Enabled Vehicular Networks
The existing computation and communication (2C) optimization schemes for
vehicular edge computing (VEC) networks mainly focus on the physical domain
without considering the influence from the social domain. This may greatly
limit the potential of task offloading, making it difficult to fully boom the
task offloading rate with given power, resulting in low energy efficiency (EE).
To address the issue, this letter devotes itself to investigate
social-mobility-aware VEC framework and proposes a novel EE-oriented 2C
assignment scheme. In doing so, we assume that the task vehicular user (T-VU)
can offload computation tasks to the service vehicular user (S-VU) and the road
side unit (RSU) by non-orthogonal multiple access (NOMA). An optimization
problem is formulated to jointly assign the 2C resources to maximize the system
EE, which turns out to be a mixed integer non-convex objective function. To
solve the problem, we transform it into separated computation and communication
resource allocation subproblems. Dealing with the first subproblem, we propose
a social-mobility-aware edge server selection and task splitting algorithm
(SM-SSTSA) to achieve edge server selection and task splitting. Then, by
solving the second subproblem, the power allocation and spectrum assignment
solutions are obtained utilizing a tightening lower bound method and a
Kuhn-Munkres algorithm. Finally, we solve the original problem through an
iterative method. Simulation results demonstrate the superior EE performance of
the proposed scheme
Robust Beamforming and Rate-Splitting Design for Next Generation Ultra-Reliable and Low-Latency Communications
The next generation ultra-reliable and low-latency communications (xURLLC)
need novel design to provide satisfactory services to the emerging
mission-critical applications. To improve the spectrum efficiency and enhance
the robustness of xURLLC, this paper proposes a robust beamforming and
rate-splitting design in the finite blocklength (FBL) regime for downlink
multi-user multi-antenna xURLLC systems. In the design, adaptive rate-splitting
is introduced to flexibly handle the complex inter-user interference and thus
improve the spectrum efficiency. Taking the imperfection of the channel state
information at the transmitter (CSIT) into consideration, a max-min user rate
problem is formulated to optimize the common and private beamforming vectors
and the rate-splitting vector under the premise of ensuring the requirements of
transmission latency and reliability of all the users. The optimization problem
is intractable due to the non-convexity of the constraint set and the infinite
constraints caused by CSIT uncertainties. To solve it, we convert the infinite
constraints into finite ones by the S-Procedure method and transform the
original problem into a difference of convex (DC) programming. A constrained
concave convex procedure (CCCP) and the Gaussian randomization based iterative
algorithm is proposed to obtain a local minimum. Simulation results confirm the
convergence, robustness and effectiveness of the proposed robust beamforming
and rate-splitting design in the FBL regime. It is also shown that the proposed
robust design achieves considerable performance gain in the worst user rate
compared with existing transmission schemes under various blocklength and block
error rate requirements.Comment: 12 pages, 9 figure
Compound Identification Using Penalized Linear Regression on Metabolomics
Compound identification is often achieved by matching the experimental mass spectra to the mass spectra stored in a reference library based on mass spectral similarity. Because the number of compounds in the reference library is much larger than the range of mass-to-charge ratio (m/z) values so that the data become high dimensional data suffering from singularity. For this reason, penalized linear regressions such as ridge regression and the lasso are used instead of the ordinary least squares regression. Furthermore, two-step approaches using the dot product and Pearson’s correlation along with the penalized linear regression are proposed in this study
Clinical efficacy of apatinib as a second-line treatment for advanced pancreatic cancer in a Chinese tertiary cancer health facility
Purpose: To study the effectiveness and safety of apatinib as second-line treatment for advanced pancreatic cancer (APC) in a Chinese tertiary cancer hospital.
Methods: Two groups of APC patients who received treatment with single-agent or two-drug combination of gemcitabine-based first-line therapy (50 per group) in The Affiliated Cancer Hospital of Nanjing Medical University, Nanjing were assessed. The study group received apatinib at or above the second line treatment, while the control group was treated with second-line chemotherapy, which was different from first-line single-drug chemotherapy. Patients received treatments until there was improvement in their conditions, or until adverse reactions became intolerable. Complete remission (CR), partial remission (PR), disease stabilization (SD), disease progression (PD), incidence of adverse reactions, and progression-free survival (PFS) of the patients were recorded.
Results: The number of PR cases in APC patients who received apatinib as second-line therapy, and the number of PD patients were higher than the corresponding populations in the control group (p < 0.05). Treatment effectiveness was significantly higher in study group patients than in control subjects (p < 0.05). However, the incidence of adverse reactions was lower in the study group than in control group. Median PFS in the study group (5 months) was significantly higher than that of the control group (4.1 months, p < 0.05).
Conclusion: The clinical efficacy of apatinib as second-line treatment for advanced pancreatic cancer is higher than that of the single drug. Apatinib is associated with low incidence of adverse reactions which prolongs PFS. Thus, apatinib has potentials for the clinical management of pancreatic cancer
First identification of primary nanoparticles in the aggregation of HMF
5-Hydroxymethylfurfural [HMF] is an important intermediate compound for fine chemicals. It is often obtained via hydrothermal treatment of biomass-derived carbohydrates, such as fructose, glucose and sucrose. This study investigates the formation of carbonaceous spheres from HMF created by dehydration of fructose under hydrothermal conditions. The carbonaceous spheres, ranging between 0.4 and 10 μm in diameter, have granulated morphologies both on the surface and in the interior. The residual solution is found to contain a massive number of primary nanoparticles. The chemical structure of the carbonaceous spheres was characterised by means of FTIR and NMR spectroscopies. Based on these observations, a mechanism involving the formation and aggregation of the nanoparticles is proposed. This mechanism differs considerably from the conventional understanding in the open literature
Cooperative Beamforming Design for Multiple RIS-Assisted Communication Systems
Reconfigurable intelligent surface (RIS) provides a promising way to build
programmable wireless transmission environments. Owing to the massive number of
controllable reflecting elements on the surface, RIS is capable of providing
considerable passive beamforming gains. At present, most related works mainly
consider the modeling, design, performance analysis and optimization of
single-RIS-assisted systems. Although there are a few of works that investigate
multiple RISs individually serving their associated users, the cooperation
among multiple RISs is not well considered as yet. To fill the gap, this paper
studies a cooperative beamforming design for multi-RIS-assisted communication
systems, where multiple RISs are deployed to assist the downlink communications
from a base station to its users. To do so, we first model the general channel
from the base station to the users for arbitrary number of reflection links.
Then, we formulate an optimization problem to maximize the sum rate of all
users. Analysis shows that the formulated problem is difficult to solve due to
its non-convexity and the interactions among the decision variables. To solve
it effectively, we first decouple the problem into three disjoint subproblems.
Then, by introducing appropriate auxiliary variables, we derive the closed-form
expressions for the decision variables and propose a low-complexity cooperative
beamforming algorithm. Simulation results have verified the effectiveness of
the proposed algorithm through comparison with various baseline methods.
Furthermore, these results also unveil that, for the sum rate maximization,
distributing the reflecting elements among multiple RISs is superior to
deploying them at one single RIS
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