Link-Node Characterization for Energy-Efficient Communication in a Static Random Wireless Sensor Network

Studies of wireless networks often work with a relatively high communication range so that each node typically communicates with a high number of neighbors. This is necessary, with a random placement, to avoid loss of coverage or connectivity. However, communicating through remote neighbors requires more energy, which can be a severe disadvantage since energy is often critical in this type of network. By comparing two-ranges, one to ensure coverage and one to save energy, we identify link-nodes which play an essential role to keep the network connected. Characterizing these nodes and their occurrence in communication routes will help to save energy and increase lifetime of the overall network. Without precautions, these link-nodes receive a high traffic load. Using simulations we find that slightly longer routes can avoid link-nodes and thus reduce average energy consumption. Network lifetime can be extended by identifying these nodes at startup and reducing their energy consumption wherever possible.     

Solution‐Processed Nickel Oxide Hole Transport Layers in High Efficiency Polymer Photovoltaic Cells

The detailed characterization of solution‐derived nickel (II) oxide (NiO) hole‐transporting layer (HTL) films and their application in high efficiency organic photovoltaic (OPV) cells is reported. The NiO precursor solution is examined in situ to determine the chemical species present. Coordination complexes of monoethanolamine (MEA) with Ni in ethanol thermally decompose to form non‐stoichiometric NiO. Specifically, the [Ni(MEA)₂(OAc)]⁺ ion is found to be the most prevalent species in the precursor solution. The defect‐induced Ni³⁺ ion, which is present in non‐stoichiometric NiO and signifies the p‐type conduction of NiO, as well as the dipolar nickel oxyhydroxide (NiOOH) species are confirmed using X‐ray photoelectron spectroscopy. Bulk heterojunction (BHJ) solar cells with a polymer/fullerene photoactive layer blend composed of poly‐dithienogermole‐thienopyrrolodione (pDTG‐TPD) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) are fabricated using these solution‐processed NiO films. The resulting devices show an average power conversion efficiency (PCE) of 7.8%, which is a 15% improvement over devices utilizing a poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL. The enhancement is due to the optical resonance in the solar cell and the hydrophobicity of NiO, which promotes a more homogeneous donor/acceptor morphology in the active layer at the NiO/BHJ interface. Finally, devices incorporating NiO as a HTL are more stable in air than devices using PEDOT:PSS.     

Impact of additive noise on system performance of a digital X-ray imaging system

The impact of additive noise on the performance of a digital X-ray imaging system was investigated. The X-ray system is uniquely designed for small animal studies with a focal spot of 20 microm and an adjustable source-to-object distance for radiography. The noise power spectrum and the detective quantum efficiency of this system were measured. The additive noise increased rapidly when the exposure time exceeded a certain range, since the charge-coupled devices of the detector had no cooling system. The noise power spectrum for the additive noise and the noise of the entire imaging system were studied and compared at different exposure times. The detective quantum efficiency was also measured at different exposure times. It was observed that for exposure times less than 10 s, the detective quantum efficiency ((DQE)(0)) is approximately 0.26, dropping to 0.13 at 4 lp/mm and to 0.026 at 8 lp/mm. However, when the exposure exceeds a certain limit (10 s in this study), the rapidly increased additive noise caused the system to be no longer quantum noise limited, resulting in a decreased detective quantum efficiency and a degraded system performance. For example, at an exposure of 20 s, the DQE(O) is approximately 0.22, dropping to 0.11 at 3 lp/mm and to 0.022 at 8 lp/mm.     

A Review on Thin-film Sensing with Terahertz Waves

In the past two decades, the development and steady improvement of terahertz technology has motivated a wide range of scientific studies designed to discover and develop terahertz applications. Terahertz sensing is one such application, and its continued maturation is virtually guaranteed by the unique properties that materials exhibit in the terahertz frequency range. Thin-film sensing is one branch of this effort that has enjoyed diverse development in the last decade. Deeply subwavelength sample thicknesses impose great difficulties to conventional terahertz spectroscopy, yet sensing those samples is essential for a large number of applications. In this article we review terahertz thin-film sensing, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy.     

Multi-heterojunction large area HgCdTe long wavelength infrared photovoltaic detector for operation at near room temperatures

This paper describes a new multi-heterojunction n ⁺pp photovoltaic infrared photodetector. The device has been developed specifically for operation at temperatures of 200–300K in the long wavelength (8–14 μm) range of the infrared spectrum. The new structure solves the perennial problems of poor quantum efficiency and low dynamic resistance found in conventional long wavelength infrared photovoltaic detectors when operated near room temperature. Computer simulations show that devices with properly optimized multiple heterojunctions are capable of achieving the performance limits imposed by the statistical nature of thermal generation-recombination processes. In order to demonstrate the technology, multiple heterojunction devices have been fabricated on epilayers grown by isothermal vapor phase epitaxy of HgCdTe and in situ As p-type doping. The detector structures were formed using a combination of conventional dry etching, angled ion milling, and angled thermal evaporation for contact metal deposition. These multi-junction n ⁺pp HgCdTe heterostructure devices exhibit performances which make them useful for many applications. D* of optically immersed multiple heterostructure photovoltaic detectors exceeding 10⁸cmHz^1/2/W were measured at λ=10.6 μm and T=300K.     

Non‐Covalent Functionalization of Graphene Using Self‐Assembly of Alkane‐Amines

A simple, versatile method for non‐covalent functionalization of graphene based on solution‐phase assembly of alkane‐amine layers is presented. Second‐order Møller–Plesset (MP2) perturbation theory on a cluster model (methylamine on pyrene) yields a binding energy of ≈220 meV for the amine–graphene interaction, which is strong enough to enable formation of a stable aminodecane layer at room temperature. Atomistic molecular dynamics simulations on an assembly of 1‐aminodecane molecules indicate that a self‐assembled monolayer can form, with the alkane chains oriented perpendicular to the graphene basal plane. The calculated monolayer height (≈1.7 nm) is in good agreement with atomic force microscopy data acquired for graphene functionalized with 1‐aminodecane, which yield a continuous layer with mean thickness ≈1.7 nm, albeit with some island defects. Raman data also confirm that self‐assembly of alkane‐amines is a non‐covalent process, i.e., it does not perturb the sp² hybridization of the graphene. Passivation and adsorbate n‐doping of graphene field‐effect devices using 1‐aminodecane, as well as high‐density binding of plasmonic metal nanoparticles and seeded atomic layer deposition of inorganic dielectrics using 1,10‐diaminodecane are also reported.     

Dynamic Force Measurement at the Microgram Level, with Application to Myofibrils of Striated Muscle

We describe a system for measurement of the dynamic mechanical properties of small bundles of myofibrils of muscle. Underwater fiber-optic sensing of tension via displacement of a quartz beam has been accomplished with a noise level of about 100 nanoNewtons in a bandwidth of 1 to 40 Hz.     

Fractal feature analysis and classification in medical imaging

Following B.B. Mandelbrot's fractal theory (1982), it was found that the fractal dimension could be obtained in medical images by the concept of fractional Brownian motion. An estimation concept for determination of the fractal dimension based upon the concept of fractional Brownian motion is discussed. Two applications are found: (1) classification; (2) edge enhancement and detection. For the purpose of classification, a normalized fractional Brownian motion feature vector is defined from this estimation concept. It represented the normalized average absolute intensity difference of pixel pairs on a surface of different scales. The feature vector uses relatively few data items to represent the statistical characteristics of the medial image surface and is invariant to linear intensity transformation. For edge enhancement and detection application, a transformed image is obtained by calculating the fractal dimension of each pixel over the whole medical image. The fractal dimension value of each pixel is obtained by calculating the fractal dimension of 7x7 pixel block centered on this pixel.     

Evaluation of Electrospun PCL-PLGA for Sustained Delivery of Kartogenin

In this study, kartogenin was incorporated into an electrospun blend of polycaprolactone and poly(lactic-co-glycolic acid) (1:1) to determine the feasibility of this system for sustained drug delivery. Kartogenin is a small-molecule drug that could enhance the outcome of microfracture, a cartilage restoration procedure, by selectively stimulating chondrogenic differentiation of endogenous bone marrow mesenchymal stem cells. Experimental results showed that kartogenin did not affect the electrospinnability of the polymer blend, and it had negligible effects on fiber morphology and scaffold mechanical properties. The loading efficiency of kartogenin into electrospun membranes was nearly 100%, and no evidence of chemical reaction between kartogenin and the polymers was detected by Fourier transform infrared spectroscopy. Analysis of the released drug using high-performance liquid chromatography–photodiode array detection indicated an abundance of kartogenin and only a small amount of its major hydrolysis product. Kartogenin displayed a typical biphasic release profile, with approximately 30% being released within 24 h followed by a much slower, constant rate of release up to 28 days. Although additional development is needed to tune the release kinetics and address issues common to electrospun scaffolds (e.g., high fiber density), the results of this study demonstrated that a scaffold electrospun from biodegradable synthetic polymers is a suitable kartogenin delivery vehicle.