Neck failure following pathologically node-negative neck dissection (pN0) in oral squamous cell carcinoma: a systematic review and meta-analysis.

Due to the risk of occult cervical metastasis, elective neck dissection (END) is recommended in the management of patients with early oral cavity squamous cell carcinoma (OSCC) and a clinically node-negative (cN0) neck. This paper presents a systematic review and meta-analysis of studies that recorded isolated regional recurrence (RR) in the pathologically node-negative neck dissection (pN0) neck following END in order to quantify the failure rate. Pubmed and Ovid databases were systematically searched for relevant articles published between January 2009 and January 2019. Studies reporting RR following END in patients with OSCC who had no pathological evidence of lymph node metastasis were eligible for inclusion in this meta-analysis. In addition, a selection of large head and neck units were invited to submit unpublished data. Search criteria produced a list of 5448 papers, of which 18 studies met the inclusion criteria. Three institutions contributed unpublished data. This included a total of 4824 patients with median follow-up of 34 months (2.8 years). Eight datasets included patients staged T1-T4 with RR 17.3% (469/2711), 13 datasets included patients staged T1-T2 with RR 7.5% (158/2113). Overall across all 21 studies, isolated neck recurrence was identified in 627 cases giving a RR of 13.0% (627/4824) on meta-analysis. Understanding the therapeutic effectiveness of END provides context for evaluation of clinical management of the cN0 in these patients. A pathologically negative neck does not guarantee against future recurrence.

An elastic-net penalized expectile regression with applications.

To perform variable selection in expectile regression, we introduce the elastic-net penalty into expectile regression and propose an elastic-net penalized expectile regression (ER-EN) model. We then adopt the semismooth Newton coordinate descent (SNCD) algorithm to solve the proposed ER-EN model in high-dimensional settings. The advantages of ER-EN model are illustrated via extensive Monte Carlo simulations. The numerical results show that the ER-EN model outperforms the elastic-net penalized least squares regression (LSR-EN), the elastic-net penalized Huber regression (HR-EN), the elastic-net penalized quantile regression (QR-EN) and conventional expectile regression (ER) in terms of variable selection and predictive ability, especially for asymmetric distributions. We also apply the ER-EN model to two real-world applications: relative location of CT slices on the axial axis and metabolism of tacrolimus (Tac) drug. Empirical results also demonstrate the superiority of the ER-EN model.

Fourier optics of image formation in aberration-corrected LEEM.

We present the extended Fourier Optics (FO) approach for modeling image formation in aberration-corrected low energy electron microscopy (ac-LEEM). The FO formalism is also generalized for image simulations of one or two-dimensional objects in ac and uncorrected (nac) LEEM. A comparison is made of the extended FO approach presented here and the extended contrast transfer function (CTF) approach for ac-LEEM that was developed earlier. The mathematically rigorous extended FO approach gains an advantage under conditions, particularly defocus, that partial coherence of the illumination may compromise the validity of the approximate CTF intensity calculation. The drawback of the FO approach compared to the CTF approach, which is its slow computational speed, is mitigated partly here by the implementation of a multi-core, multi-threading programming architecture. This work broadens our capabilities to understand the origins of LEEM image contrast and to perform quantitative evaluation of contrast observed in an image focal series.

High throughput scanning µLEED imaging of surface structural heterogeneity: Defective graphene on Cu(111).

Micro-low energy electron diffraction (µLEED) is frequently used in conjunction with low energy electron microscopy (LEEM) to learn about local surface structural features in small selected areas. Scanning µLEED measurements performed with a very small electron beam (250 nm) can provide precise quantitative information about structural variations with high spatial resolution. We have developed the Source Extraction and Photometry (SEP) - Spot Profile Analysis (SPA) tool for evaluating scanning µLEED data with high throughput. The capability to automate diffraction peak identification with SEP-SPA opens up the possibility to investigate systems with complex diffraction patterns in which diffraction peak positions vary rapidly for small lateral displacements on the surface. The application of this tool to evaluate scanning µLEED data obtained for defective graphene on Cu(111) demonstrates its capabilities. A rich rotational domain structure is observed in which a majority of the graphene is co-aligned with the Cu(111) substrate and the significant remainder comprises domains with large rotations and small sizes that are comparable to the small beam size.

One-step generation of hybrid micro-optics with high-frequency diffractive structures on infrared materials by ultra-precision side milling.

Hybrid micro-optics of infrared (IR) materials are of great advantage in realizing the function integration and minimization of advanced IR optical systems. However, due to the hard-and-brittle nature of IR materials, it is still challenging for both non-mechanical and mechanical technologies to achieve one-step generation of hybrid infrared micro-optics with high form accuracy. In the present study, a flexible method, namely ultra-precision side milling (UPSM), is first introduced to achieve one-step generation of infrared hybrid micro-optics in ductile mode, and the corresponding reflective diffraction characteristics are analyzed. In UPSM, the reflective/refractive primary surface of the hybrid micro-optics is formed via the removal of workpiece material, and the high-frequent secondary diffractive micro/nanostructures are simultaneously generated by the tool residual marks of cutting trajectories. With the consideration of the changing curvature of the primary surface, the optimal toolpath generation strategy is introduced to acquire the desired shapes of the secondary micro/nanostructures, and the selecting criteria of the machining parameters is discussed to avoid the brittle fractures of IR materials. In practice, two types of hybrid micro-optic components, namely hybrid micro-aspheric arrays and sinusoid grid surface with high-frequent secondary unidirectional phase gratings, are successfully fabricated on single-crystal silicon to validate the proposed method. The method adopted in this study is very promising for the deterministic fabrication of hybrid micro-optics on infrared materials.

Comparing Fourier optics and contrast transfer function modeling of image formation in low energy electron microscopy.

A theoretical understanding of image formation in cathode lens microscopy can facilitate image interpretation. We compare Fourier Optics (FO) and Contrast Transfer Function (CTF) approaches that were recently adapted from other realms of microscopy to model image formation in low energy electron microscopy (LEEM). Although these two approaches incorporate imaging errors from several sources similarly, they differ in the way that the image intensity is calculated. The simplification that is used in the CTF calculation advantageously leads to its computational efficiency. However, we find that lens aberrations, and spatial and temporal coherence may affect the validity of the CTF approach to model LEEM image formation under certain conditions. In particular, these effects depend strongly on the nature of the object being imaged and also become more pronounced with increasing defocus. While the use of the CTF approach appears to be justified for objects that are routinely imaged with LEEM, comparison of theory to experimental observations of a focal image series for rippled, suspended graphene reveals one example where FO works, but CTF does not. This work alerts us to potential pitfalls and guides the effective use of FO and CTF approaches. It also lays the foundation for quantitative image evaluation using these methods.

Multicolor emission from intermediate band semiconductor ZnO1-xSex.

Photoluminescence and photomodulated reflectivity measurements of ZnOSe alloys are used to demonstrate a splitting of the valence band due to the band anticrossing interaction between localized Se states and the extended valence band states of the host ZnO matrix. A strong multiband emission associated with optical transitions from the conduction band to lower E- and upper E+ valence subbands has been observed at room temperature. The composition dependence of the optical transition energies is well explained by the electronic band structure calculated using the kp method combined with the band anticrossing model. The observation of the multiband emission is possible because of relatively long recombination lifetimes. Longer than 1 ns lifetimes for holes photoexcited to the lower valence subband offer a potential of using the alloy as an intermediate band semiconductor for solar power conversion applications.

Improved ion implant fluence uniformity in hydrogen enhanced glow discharge plasma immersion ion implantation into silicon.

Enhanced glow discharge plasma immersion ion implantation does not require an external plasma source but ion focusing affects the lateral ion fluence uniformity, thereby hampering its use in high-fluence hydrogen ion implantation for thin film transfer and fabrication of silicon-on-insulator. Insertion of a metal ring between the sample stage and glass chamber improves the ion uniformity and reduces the ion fluence non-uniformity as the cathode voltage is raised. Two-dimensional multiple-grid particle-in-cell simulation confirms that the variation of electric field inside the chamber leads to mitigation of the ion focusing phenomenon and the results are corroborated experimentally by hydrogen forward scattering.

Controlling the Curie temperature in (Ga,Mn)As through location of the Fermi level within the impurity band.

The ferromagnetic semiconductor (Ga,Mn)As has emerged as the most studied material for prototype applications in semiconductor spintronics. Because ferromagnetism in (Ga,Mn)As is hole-mediated, the nature of the hole states has direct and crucial bearing on its Curie temperature T(C). It is vigorously debated, however, whether holes in (Ga,Mn)As reside in the valence band or in an impurity band. Here we combine results of channelling experiments, which measure the concentrations both of Mn ions and of holes relevant to the ferromagnetic order, with magnetization, transport, and magneto-optical data to address this issue. Taken together, these measurements provide strong evidence that it is the location of the Fermi level within the impurity band that determines T(C) through determining the degree of hole localization. This finding differs drastically from the often accepted view that T(C) is controlled by valence band holes, thus opening new avenues for achieving higher values of T(C).

Engineering the electronic band structure for multiband solar cells.

Using the unique features of the electronic band structure of GaN(x)As(1-x) alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the band anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

Embedded binary eutectic alloy nanostructures: a new class of phase change materials.

Phase change materials are essential to a number of technologies ranging from optical data storage to energy storage and transport applications. This widespread interest has given rise to a substantial effort to develop bulk phase change materials well suited for desired applications. Here, we suggest a novel and complementary approach, the use of binary eutectic alloy nanoparticles embedded within a matrix. Using GeSn nanoparticles embedded in silica as an example, we establish that the presence of a nanoparticle/matrix interface enables one to stabilize both nanobicrystal and homogeneous alloy morphologies. Further, the kinetics of switching between the two morphologies can be tuned simply by altering the composition.

Catalytic coupling of CO2 with epoxide over supported and unsupported amines.

Catalytic coupling of carbon dioxide with epoxide to cyclic carbonate is an important reaction that has recently been receiving renewed interest. This route allows the use of carbon dioxide as a greener chemical feedstock, which challenges the current practices for the synthesis of cyclic carbonates and derivatives. The present study is mainly concerned with catalytic coupling reaction between CO(2) and propylene oxide using organic amine as catalyst. The structural aspects of amines and the effects of their immobilization on solid surfaces on reaction kinetics are particularly studied. It is found that 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) amine maintains high catalytic activity both with and without solid support, but other primary amines, such as p-phenylenediamine give much reduced activity when placed on a solid surface. It is attributed to the absence of surface hydrogen in the supported TBD, prohibiting the catalyst sites from CO(2) poisoning. The coupling of other epoxides, including epichlorohydrin and styrene oxide over the solid supported amine, is also briefly carried out. Reaction mechanisms are proposed to explain the experimental observations.

Metal-insulator transition by isovalent anion substitution in Ga1-xMnxAs: implications to ferromagnetism.

We have investigated the effect of partial isovalent anion substitution in Ga1-xMnxAs on electrical transport and ferromagnetism. Substitution of only 2.4% of As by P induces a metal-insulator transition at a constant Mn doping of x=0.046 while the replacement of 0.4% As with N results in the crossover from metal to insulator for x=0.037. This remarkable behavior is consistent with a scenario in which holes located within an impurity band are scattered by alloy disorder in the anion sublattice. The shorter mean free path of holes, which mediate ferromagnetism, reduces the Curie temperature T_{C} from 113 to 60 K (100 to 65 K) upon the introduction of 3.1% P (1% N) into the As sublattice.

Engineering preformed cobalt-doped platinum nanocatalysts for ultraselective hydrogenation.

Bimetallic heterostructures are used as industrial catalysts for many important transformations. However, conventional catalysts are primarily prepared in cost-effective manners without much appreciation in metal size control and metal-metal interaction. By employing recent nanotechnology, Pt nanocrystals with tailored sizes can be decorated with Co atoms in a controlled manner in colloid solution as preformed nanocatalysts before they are applied on support materials. Thus, we show that the terminal CO hydrogenation can be achieved in high activity, while the undesirable hydrogenation of the CC group can be totally suppressed in the selective hydrogenation of alpha,beta-unsaturated aldehydes to unsaturated alcohols, when Co decorated Pt nanocrystals within a critical size range are used. This is achieved through blockage of unselective low coordination sites and the optimization in electronic influence of the Pt nanoparticle of appropriate size by the Co decoration. This work clearly demonstrates the advantage in engineering preformed nanoparticles via a bottom-up construction and illustrates that this route of catalyst design may lead to improved catalytic processes.

Evidence for p-type doping of InN.

The first evidence of successful p-type doping of InN is presented. It is shown that InN:Mg films consist of a p-type bulk region with a thin n-type inversion layer at the surface that prevents electrical contact to the bulk. Capacitance-voltage measurements indicate a net concentration of ionized acceptors below the -type surface. Irradiation with 2 MeV He+ ions is used to convert the bulk of InN:Mg from p to n-type, at which point photoluminescence is recovered. The conversion is well explained by a model assuming two parallel conducting layers (the surface and the bulk) in the films.

Ferromagnetism in Ga(1-x)Mn(x)P: evidence for inter-Mn exchange mediated by localized holes within a detached impurity band.

We report an energy gap for hole photoexcitation in ferromagnetic Ga(1-x)Mn(x)P that is tunable by Mn concentration (x < or = 0.06) and by compensation with Te donors. For x approximately 0.06, electrical transport is dominated by excitation across this gap above the Curie temperature (TC) of 60 K and by thermally activated hopping below TC. Magnetization measurements reveal a moment of 3.9 +/- 0.4 muB per substitutional Mn while the large anomalous Hall signal demonstrates that the ferromagnetism is carrier mediated. In aggregate these data indicate that ferromagnetic exchange is mediated by holes localized in a Mn-derived band that is detached from the valence band.

Diluted II-VI oxide semiconductors with multiple band gaps.

We report the realization of a new mult-band-gap semiconductor. Zn(1-y)Mn(y)OxTe1-x alloys have been synthesized using the combination of oxygen ion implantation and pulsed laser melting. Incorporation of small quantities of isovalent oxygen leads to the formation of a narrow, oxygen-derived band of extended states located within the band gap of the Zn(1-y)Mn(y)Te host. When only 1.3% of Te atoms are replaced with oxygen in a Zn0.88Mn0.12Te crystal the resulting band structure consists of two direct band gaps with interband transitions at approximately 1.77 and 2.7 eV. This remarkable modification of the band structure is well described by the band anticrossing model. With multiple band gaps that fall within the solar energy spectrum, Zn(1-y)Mn(y)OxTe1-x is a material perfectly satisfying the conditions for single-junction photovoltaics with the potential for power conversion efficiencies surpassing 50%.

Colloidal stable silica encapsulated nano-magnetic composite as a novel bio-catalyst carrier.

A colloidal stable silica-encapsulated magnetic nano-composite of a controlled dimension is, for the first time, employed to carry beta-lactamase via chemical linkage on the silica overlayer: activity study reflects that this new type of immobilisation allows site (enzyme) isolation, accessibility as good as free enzyme and recovery & reusability upon application of magnetic separation.