bluuebunny/crossref_metadata_2025 huggingface dataset:
Interplay between translational diffusion and large-amplitude angular jumps of water molecules
Authors: Liu Chao , Zhang Yangyang , Zhang Jian , Wang Jun , Li Wenfei , Wang Wei
Published: May 2018

Understanding the microscopic mechanism of water molecular translational diffusion is a challenging topic in both physics and chemistry. Here, we report an investigation on the interplay between the translational diffusion and the large-amplitude angular jumps of water molecules in bulk water using molecular dynamics simulations. We found that large-amplitude angular jumps are tightly coupled to the translational diffusions. Particularly, we revealed that concurrent rotational jumps of spatially neighboring water molecules induce inter-basin translational jumps, which contributes to the fast component of the water translational diffusion. Consequently, the translational diffusion shows positional heterogeneity; i.e., the neighbors of the water molecules with inter-basin translational jumps have larger probability to diffuse by inter-basin translational jumps. Our control simulations showed that a model water molecule with moderate hydrogen bond strength can diffuse much faster than a simple Lennard-Jones particle in bulk water due to the capability of disturbing the hydrogen bond network of the surrounding water molecules. Our results added to the understanding of the microscopic picture of the water translational diffusion and demonstrated the unique features of water diffusion arising from their hydrogen bond network structure compared with those of the simple liquids.
Two-dimensional Fano lineshapes: Excited-state absorption contributions
Authors: Finkelstein-Shapiro Daniel , Pullerits Tõnu , Hansen Thorsten
Published: May 2018

Fano interferences in nanostructures are influenced by dissipation effects as well as many-body interactions. Two-dimensional coherent spectroscopies have just begun to be applied to these systems where the spectroscopic signatures of a discrete-continuum structure are not known. In this article, we calculate the excited-state absorption contribution for different models of higher lying excited states. We find that the characteristic asymmetry of one-dimensional spectroscopies is recovered from the many-body contributions and that the higher lying excited manifolds have distorted lineshapes that are not anticipated from discrete-level Hamiltonians. We show that the Stimulated Emission cannot have contributions from a flat continuum of states. This work completes the Ground-State Bleach and Stimulated Emission signals that were calculated previously [D. Finkelstein-Shapiro et al., Phys. Rev. B 94, 205137 (2016)]. The model reproduces the observations reported for molecules on surfaces probed by 2DIR.
Low-temperature, ultrahigh-vacuum tip-enhanced Raman spectroscopy combined with molecular beam epitaxy for in situ two-dimensional materials’ studies
Authors: Sheng Shaoxiang , Li Wenbin , Gou Jian , Cheng Peng , Chen Lan , Wu Kehui
Published: May 2018

Tip-enhanced Raman spectroscopy (TERS), which combines scanning probe microscopy with the Raman spectroscopy, is capable to access the local structure and chemical information simultaneously. However, the application of ambient TERS is limited by the unstable and poorly controllable experimental conditions. Here, we designed a high performance TERS system based on a low-temperature ultrahigh-vacuum scanning tunneling microscope (LT-UHV-STM) and combined with a molecular beam epitaxy (MBE) system. It can be used for growing two-dimensional (2D) materials and for in situ STM and TERS characterization. Using a 2D silicene sheet on the Ag(111) surface as a model system, we achieved an unprecedented 109 Raman single enhancement factor in combination with a TERS spatial resolution down to 0.5 nm. The results show that TERS combined with a MBE system can be a powerful tool to study low dimensional materials and surface science.
Fluctuation-dissipation relation and stationary distribution of an exactly solvable many-particle model for active biomatter far from equilibrium
Authors: Netz Roland R.
Published: May 2018

An exactly solvable, Hamiltonian-based model of many massive particles that are coupled by harmonic potentials and driven by stochastic non-equilibrium forces is introduced. The stationary distribution and the fluctuation-dissipation relation are derived in closed form for the general non-equilibrium case. Deviations from equilibrium are on one hand characterized by the difference of the obtained stationary distribution from the Boltzmann distribution; this is possible because the model derives from a particle Hamiltonian. On the other hand, the difference between the obtained non-equilibrium fluctuation-dissipation relation and the standard equilibrium fluctuation-dissipation theorem allows us to quantify non-equilibrium in an alternative fashion. Both indicators of non-equilibrium behavior, i.e., deviations from the Boltzmann distribution and deviations from the equilibrium fluctuation-dissipation theorem, can be expressed in terms of a single non-equilibrium parameter α that involves the ratio of friction coefficients and random force strengths. The concept of a non-equilibrium effective temperature, which can be defined by the relation between fluctuations and the dissipation, is by comparison with the exactly derived stationary distribution shown not to hold, even if the effective temperature is made frequency dependent. The analysis is not confined to close-to-equilibrium situations but rather is exact and thus holds for arbitrarily large deviations from equilibrium. Also, the suggested harmonic model can be obtained from non-linear mechanical network systems by an expansion in terms of suitably chosen deviatory coordinates; the obtained results should thus be quite general. This is demonstrated by comparison of the derived non-equilibrium fluctuation dissipation relation with experimental data on actin networks that are driven out of equilibrium by energy-consuming protein motors. The comparison is excellent and allows us to extract the non-equilibrium parameter α from experimental spectral response and fluctuation data.
Droplet states in quantum XXZ spin systems on general graphs
Authors: Fischbacher C. , Stolz G.
Published: May 2018

We study XXZ spin systems on general graphs. In particular, we describe the formation of droplet states near the bottom of the spectrum in the Ising phase of the model, where the Z-term dominates the XX-term. As key tools, we use particle number conservation of XXZ systems and symmetric products of graphs with their associated adjacency matrices and Laplacians. Of particular interest to us are strips and multi-dimensional Euclidean lattices, for which we discuss the existence of spectral gaps above the droplet regime. We also prove a Combes-Thomas bound which shows that the eigenstates in the droplet regime are exponentially small perturbations of strict (classical) droplets.
The electrical asymmetry effect in a multi frequency geometrically asymmetric capacitively coupled plasma: A study by a nonlinear global model
Authors: Saikia P. , Bhuyan H. , Escalona M. , Favre M. , Bora B. , Kakati M. , Wyndham E. , Rawat R. S. , Schulze J.
Published: May 2018

We investigate the electrical asymmetry effect (EAE) and the current dynamics in a geometrically asymmetric capacitively coupled radio frequency plasma driven by multiple consecutive harmonics based on a nonlinear global model. The discharge symmetry is controlled via the EAE, i.e., by varying the total number of harmonics and tuning the phase shifts (θk) between them. Here, we systematically study the EAE in a low pressure (4 Pa) argon discharge with different geometrical asymmetries driven by a multifrequency rf source consisting of 13.56 MHz and its harmonics. We find that the geometrical asymmetry strongly affects the absolute value of the DC self-bias voltage, but its functional dependence on θk is similar at different values of the geometrical asymmetry. Also, the values of the DC self-bias are enhanced by adding more consecutive harmonics. The voltage drop across the sheath at the powered and grounded electrode is found to increase/decrease, respectively, with the increase in the number of harmonics of the fundamental frequency. For the purpose of validating the model, its outputs are compared with the results obtained in a geometrically and electrically asymmetric 2f capacitively coupled plasmas experiment conducted by Schuengel et al. [J. Appl. Phys. 112, 053302 (2012)]. Finally, we study the self-excitation of nonlinear plasma series resonance oscillations and its dependence on the geometrical asymmetry as well as the phase angles between the driving frequencies.
The effect of target materials on the propagation of atmospheric-pressure plasma jets
Authors: Ji Longfei , Yan Wen , Xia Yang , Liu Dongping
Published: May 2018

The current study is focused on the effect of target materials (quartz plate, copper sheet, and quartz plate with a grounded copper sheet on the back) on the propagation of atmospheric-pressure helium plasma jets. The dynamics of ionization waves (IWs) and the relative amount of reactive oxygen species (OH and O) in the IW front were compared by using spatial and temporal images and relative optical emission spectroscopy. Our measurements show that the targets can significantly affect the propagation and intensity of the IWs. In addition, strong OH emission lines were detected when the IWs impinged upon the damp surface. Numerical simulations have been carried out to explain the experimental observation. The propagation velocity of IWs predicted by the simulation was in good agreement with the experimental results. Simulation results suggest that the density and velocity of IWs mainly depend on the electric field between the high voltage electrode tip and the target. Analysis indicates that the targets could change the electric field distribution between the high voltage electrode and targets and thus affect the dynamics and the density of the IWs, the generation of reactive oxygen species, and the corresponding sterilization efficiency.
Non-empirical exchange-correlation parameterizations based on exact conditions from correlated orbital theory
Authors: Haiduke Roberto Luiz A. , Bartlett Rodney J.
Published: May 2018

Some of the exact conditions provided by the correlated orbital theory are employed to propose new non-empirical parameterizations for exchange-correlation functionals from Density Functional Theory (DFT). This reparameterization process is based on range-separated functionals with 100% exact exchange for long-range interelectronic interactions. The functionals developed here, CAM-QTP-02 and LC-QTP, show mitigated self-interaction error, correctly predict vertical ionization potentials as the negative of eigenvalues for occupied orbitals, and provide nice excitation energies, even for challenging charge-transfer excited states. Moreover, some improvements are observed for reaction barrier heights with respect to the other functionals belonging to the quantum theory project (QTP) family. Finally, the most important achievement of these new functionals is an excellent description of vertical electron affinities (EAs) of atoms and molecules as the negative of appropriate virtual orbital eigenvalues. In this case, the mean absolute deviations for EAs in molecules are smaller than 0.10 eV, showing that physical interpretation can indeed be ascribed to some unoccupied orbitals from DFT.
Effect of stacking faults on the photoluminescence spectrum of zincblende GaN
Authors: Church S. A. , Hammersley S. , Mitchell P. W. , Kappers M. J. , Lee L. Y. , Massabuau F. , Sahonta S. L. , Frentrup M. , Shaw L. J. , Wallis D. J. , Humphreys C. J. , Oliver R. A. , Binks D. J. , Dawson P.
Published: May 2018

The photoluminescence spectra of a zincblende GaN epilayer grown via metal-organic chemical vapour deposition upon 3C-SiC/Si (001) substrates were investigated. Of particular interest was a broad emission band centered at 3.4 eV, with a FWHM of 200 meV, which extends above the bandgap of both zincblende and wurtzite GaN. Photoluminescence excitation measurements show that this band is associated with an absorption edge centered at 3.6 eV. Photoluminescence time decays for the band are monoexponential, with lifetimes that reduce from 0.67 ns to 0.15 ns as the recombination energy increases. TEM measurements show no evidence of wurtzite GaN inclusions which are typically used to explain emission in this energy range. However, dense stacking fault bunches are present in the epilayers. A model for the band alignment at the stacking faults was developed to explain this emission band, showing how both electrons and holes can be confined adjacent to stacking faults. Different stacking fault separations can change the carrier confinement energies sufficiently to explain the width of the emission band, and change the carrier wavefunction overlap to account for the variation in decay time.
Perspective: Memcomputing: Leveraging memory and physics to compute efficiently
Authors: Di Ventra Massimiliano , Traversa Fabio L.
Published: May 2018

It is well known that physical phenomena may be of great help in computing some difficult problems efficiently. A typical example is prime factorization that may be solved in polynomial time by exploiting quantum entanglement on a quantum computer. There are, however, other types of (non-quantum) physical properties that one may leverage to compute efficiently a wide range of hard problems. In this perspective, we discuss how to employ one such property, memory (time non-locality), in a novel physics-based approach to computation: Memcomputing. In particular, we focus on digital memcomputing machines (DMMs) that are scalable. DMMs can be realized with non-linear dynamical systems with memory. The latter property allows the realization of a new type of Boolean logic, one that is self-organizing. Self-organizing logic gates are “terminal-agnostic,” namely, they do not distinguish between the input and output terminals. When appropriately assembled to represent a given combinatorial/optimization problem, the corresponding self-organizing circuit converges to the equilibrium points that express the solutions of the problem at hand. In doing so, DMMs take advantage of the long-range order that develops during the transient dynamics. This collective dynamical behavior, reminiscent of a phase transition, or even the “edge of chaos,” is mediated by families of classical trajectories (instantons) that connect critical points of increasing stability in the system's phase space. The topological character of the solution search renders DMMs robust against noise and structural disorder. Since DMMs are non-quantum systems described by ordinary differential equations, not only can they be built in hardware with the available technology, they can also be simulated efficiently on modern classical computers. As an example, we will show the polynomial-time solution of the subset-sum problem for the worst cases, and point to other types of hard problems where simulations of DMMs' equations of motion on classical computers have already demonstrated substantial advantages over traditional approaches. We conclude this article by outlining further directions of study.
Poly-crystalline silicon-oxide films as carrier-selective passivating contacts for c-Si solar cells
Authors: Yang Guangtao , Guo Peiqing , Procel Paul , Weeber Arthur , Isabella Olindo , Zeman Miro
Published: May 2018

The poly-Si carrier-selective passivating contacts (CSPCs) parasitically absorb a substantial amount of light, especially in the form of free carrier absorption. To minimize these losses, we developed CSPCs based on oxygen-alloyed poly-Si (poly-SiOx) and deployed them in c-Si solar cells. Transmission electron microscopy analysis indicates the presence of nanometer-scale silicon crystals within such poly-SiOx layers. By varying the O content during material deposition, we can manipulate the crystallinity of the poly-SiOx material and its absorption coefficient. Also, depending on the O content, the bandgap of the poly-SiOx material can be widened, making it transparent for longer wavelength light. Thus, we optimized the O alloying, doping, annealing, and hydrogenation conditions. As a result, an extremely high passivation quality for both n-type poly-SiOx (J0 = 3.0 fA/cm2 and iVoc = 740 mV) and p-type poly-SiOx (J0 = 17.0 fA/cm2 and iVoc = 700 mV) is obtained. A fill factor of 83.5% is measured in front/back-contacted solar cells with both polarities made up of poly-SiOx. This indicates that the carrier transport through the junction between poly-SiOx and c-Si is sufficiently efficient. To demonstrate the merit of poly-SiOx layers' high transparency at long wavelengths, they are deployed at the back side of interdigitated back-contacted (IBC) solar cells. A preliminary cell efficiency of 19.7% is obtained with much room for further improvement. Compared to an IBC solar cell with poly-Si CSPCs, a higher internal quantum efficiency at long wavelengths is observed for the IBC solar cell with poly-SiOx CSPCs, thus demonstrating the potential of poly-SiOx in enabling higher JSC.
Spin-orbit torques in high-resistivity-W/CoFeB/MgO
Authors: Takeuchi Yutaro , Zhang Chaoliang , Okada Atsushi , Sato Hideo , Fukami Shunsuke , Ohno Hideo
Published: May 2018

Magnetic heterostructures consisting of high-resistivity (238 ± 5 µΩ cm)-W/CoFeB/MgO are prepared by sputtering and their spin-orbit torques are evaluated as a function of W thickness through an extended harmonic measurement. W thickness dependence of the spin-orbit torque with the Slonczewski-like symmetry is well described by the drift-diffusion model with an efficiency parameter, the so-called effective spin Hall angle, of −0.62 ± 0.03. In contrast, the field-like spin-orbit torque is one order of magnitude smaller than the Slonczewski-like torque and shows no appreciable dependence on the W thickness, suggesting a different origin from the Slonczewski-like torque. The results indicate that high-resistivity W is promising for low-current and reliable spin-orbit torque-controlled devices.
Role of electron-phonon coupling and thermal expansion on band gaps, carrier mobility, and interfacial offsets in kesterite thin-film solar cells
Authors: Monserrat Bartomeu , Park Ji-Sang , Kim Sunghyun , Walsh Aron
Published: May 2018

The efficiencies of solar cells based on kesterite Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) are limited by a low open-circuit voltage due to high rates of non-radiative electron-hole recombination. To probe the origin of this bottleneck, we calculate the band offset of CZTS(Se) with CdS, confirming a weak spike of 0.1 eV for CZTS/wurtzite-CdS and a strong spike of 0.4 eV for CZTSe/wurtzite-CdS. We also consider the effects of temperature on the band alignment, finding that increasing temperature significantly enhances the spike-type offset. We further resolve an outstanding discrepancy between the measured and calculated phonon frequencies for the kesterites, and use these to estimate the upper limit of electron and hole mobilities based on optic phonon Fröhlich scattering, which uncovers an intrinsic asymmetry with faster (minority carrier) electron mobility.
Elucidation of the atomic-scale mechanism of the anisotropic oxidation rate of 4H-SiC between the (0001) Si-face and (0001¯) C-face by using a new Si-O-C interatomic potential
Authors: Takamoto So , Yamasaki Takahiro , Ohno Takahisa , Kaneta Chioko , Hatano Asuka , Izumi Satoshi
Published: May 2018

Silicon carbide (SiC) is an attractive semiconductor material for applications in power electronic devices. However, fabrication of a high-quality SiC/SiO2 interface has been a challenge. It is well-known that there is a great difference in the oxidation rate between the Si-face and the C-face and that the quality of oxide on the Si-face is greater than that on the C-face. However, the atomistic mechanism of the thermal oxidation of SiC remains to be solved. In this paper, a new Si-O-C interatomic potential was developed to reproduce the kinetics of the thermal oxidation of SiC. Using this newly developed potential, large-scale SiC oxidation simulations at various temperatures were performed. The results showed that the activation energy of the Si-face is much larger than that of the C-face. In the case of the Si-face, a flat and aligned interface structure including Si1+ was created. Based on the estimated activation energies of the intermediate oxide states, it is proposed that the stability of the flat interface structure is the origin of the high activation energy of the oxidation of the Si-face. In contrast, in the case of the C-face, it is found that the Si atom at the interface is easily pulled up by the O atoms. This process generates the disordered interface and decreases the activation energy of the oxidation. It is also proposed that many excess C atoms are created in the case of the C-face.
Attacker-defender game from a network science perspective
Authors: Li Ya-Peng , Tan Suo-Yi , Deng Ye , Wu Jun
Published: May 2018

Dealing with the protection of critical infrastructures, many game-theoretic methods have been developed to study the strategic interactions between defenders and attackers. However, most game models ignore the interrelationship between different components within a certain system. In this paper, we propose a simultaneous-move attacker-defender game model, which is a two-player zero-sum static game with complete information. The strategies and payoffs of this game are defined on the basis of the topology structure of the infrastructure system, which is represented by a complex network. Due to the complexity of strategies, the attack and defense strategies are confined by two typical strategies, namely, targeted strategy and random strategy. The simulation results indicate that in a scale-free network, the attacker virtually always attacks randomly in the Nash equilibrium. With a small cost-sensitive parameter, representing the degree to which costs increase with the importance of a target, the defender protects the hub targets with large degrees preferentially. When the cost-sensitive parameter exceeds a threshold, the defender switches to protecting nodes randomly. Our work provides a new theoretical framework to analyze the confrontations between the attacker and the defender on critical infrastructures and deserves further study.
Fast-forward Langevin dynamics with momentum flips
Authors: Hijazi Mahdi , Wilkins David M. , Ceriotti Michele
Published: May 2018

Stochastic thermostats based on the Langevin equation, in which a system is coupled to an external heat bath, are popular methods for temperature control in molecular dynamics simulations due to their ergodicity and their ease of implementation. Traditionally, these thermostats suffer from sluggish behavior in the limit of high friction, unlike thermostats of the Nosé-Hoover family whose performance degrades more gently in the strong coupling regime. We propose a simple and easy-to-implement modification to the integration scheme of the Langevin algorithm that addresses the fundamental source of the overdamped behavior of high-friction Langevin dynamics: if the action of the thermostat causes the momentum of a particle to change direction, it is flipped back. This fast-forward Langevin equation preserves the momentum distribution and so guarantees the correct equilibrium sampling. It mimics the quadratic behavior of Nosé-Hoover thermostats and displays similarly good performance in the strong coupling limit. We test the efficiency of this scheme by applying it to a 1-dimensional harmonic oscillator, as well as to water and Lennard-Jones polymers. The sampling efficiency of the fast-forward Langevin equation thermostat, measured by the correlation time of relevant system variables, is at least as good as the traditional Langevin thermostat, and in the overdamped regime, the fast-forward thermostat performs much better, improving the efficiency by an order of magnitude at the highest frictions we considered.
Medical-grade ultra-high molecular weight polyethylene: Past, current and future
Authors: Zaribaf Fedra Parnian
Published: May 2018

Ultra-high molecular weight polyethylene is a semi-crystalline polymer (45–60%) with six decades of orthopaedic applications. This polymer has a high fracture toughness (30 kJ m−2) which comes from the molecular weight and the chain entanglements. Adverse alteration of the properties may lead to the part's pre-mature failure. This paper reviews the current manufacturing methods, and their effect on the properties of the polymer. The review also focused on the attempts of enhancing the polymer properties. The main cause of failure is implant loosing owing to the polymeric wear particles. Many manufacturers have attempted to enhance the wear and oxidation properties of the polymer, and the outcome of the new technologies is critically reviewed. Finally, the review explores the potential for future developments.

This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.
Phytoplankton ecology in the Bay of Quinte, Lake Ontario: Spatial distribution, dynamics and heterogeneity
Authors: Munawar M. , Fitzpatrick M. , Niblock H. , Kling H. , Lorimer J. , Rozon R.
Published: May 2018

The Bay of Quinte, a large riverine embayment located on the northeastern shores of Lake Ontario, has a long history of cultural eutrophication. While the Bay has been the subject of an extensive research and monitoring program that began in 1972, phytoplankton assessments have been limited to 2–3 index stations with few exceptions. Our study consisted of three separate surveys conducted during the summer of 2010 (June, August, September) at 12 sites spread evenly throughout the Bay. Among the major findings were that conditions in the Bay ranged from oligo- to mesotrophic in June, but were primarily eutrophic in August and September with algal blooms observed at 50–75% of the sites; the spatial extent limited only by incursions of oligotrophic water from Lake Ontario. Furthermore, primary productivity in the Bay (e.g. 43.3–109.6 mg C m−3 h−1 in September) was among the highest reported in the Great Lakes, indicative of a phytoplankton community very well adapted to its environment. We also found that the Bay of Quinte supported a diverse algal flora containing 140 unique species in June, 209 in August and 169 in September which we attribute to the variable physical environment. Of the 35 phytoplankton samples assessed, Diatomeae were the most prevalent taxa in 16 of those assemblages followed by Cyanophyta (including many toxigenic species) in 12. The relative importance of diatoms are often overlooked in studies of eutrophication yet two species in particular, Aulacoseira granulata and A. ambigua, were major contributors to both the algal standing crop and the elevated rates of primary production. We recommend that future research be directed at understanding the ecology, physiology and dynamics of these filamentous diatoms as well as their associations with filamentous and colonial cyanobacteria.
Basic Molecular Genetics Concepts and Tools
Authors: Detera-Wadleigh Sevilla D. , Akula Nirmala , Hou Liping
Published: May 2018

Progress in genetics in the last decades has been spurred largely by the Human Genome Project. Successful sequencing of the human genome and genomes of organisms across the evolutionary scale has been achieved. Scientific discoveries and innovations steered the refinement and annotation of sequences, cataloging of variation including SNPs and CNVs, development of fast, precise, high throughput methods and improved bioinformatics and statistical tools. These advances boosted GWAS on large samples identifying multiple susceptibility loci in diverse complex diseases and traits. Exome, whole genome and RNA sequencing has uncovered intricate elements of coding, noncoding and regulatory regions and the richness of the transcriptome. Evolution in genome editing has heightened the ability to alter any nucleotide and discern its biological effect. Exploiting these innovations in studies involving cells derived from patients through the iPSC technology offers manifold possibilities for functional studies that could enhance disease modeling and yield new therapeutic targets.
Bioinformatics in Psychiatric Genetics
Authors: Mueller Nikola S. , Kondofersky Ivan , Eraslan Gökcen , Worf Karolina , Theis Fabian J.
Published: May 2018

Bioinformatics in psychiatric research is surveyed by exploring data analysis techniques tailored to extract information from genetic studies. Genome-wide association studies (GWAS) play a major role by providing links between certain psychiatric diseases and single-nucleotide polymorphisms (SNPs). A challenge in identifying such links is prioritizing SNPs, and we give an overview of state-of-the-art prioritization methods and discuss current trends. Furthermore, we give details on post-GWAS analysis by introducing network-based knowledge. The aim of incorporating network information either in the sense of local proximity or similar function, is the formulation of multivariate models where multiple SNPs may have synergistic effects on a disease that cannot be inferred univariately. Finally, we provide a list of a combination of available tools and biological databases of identified genetic associations to psychiatric diseases. These open up the possibility for researchers to use published results and thus profit from findings in their respective fields.
Next-Generation Sequencing in Genetic Studies of Psychiatric Disorders
Authors: Ramdas Shweta , Li Jun Z.
Published: May 2018

Next-generation sequencing (NGS) technologies make it possible to efficiently detect DNA variants in either entire genomes or any subsets of the genome, and have dramatically enhanced our ability to search for genetic risk factors of complex psychiatric diseases. While genotyping-based association studies focus on common variants that track extended genomic segments, NGS provides unbiased identification of both common and rare variants, including those that are functionally important but appear in very few families or sporadic cases. Thus NGS directly highlights plausible causal variants, even if such variants are extremely heterogeneous in the population. Meanwhile, such heterogeneity requires new analytical approaches that can aggregate rare variant burden over predefined functional unit such as a gene or a segment of non-coding region with presumed function. Rapid application of NGS technologies also underscored other limits in psychiatric genetics research, including the need for detailed phenotyping and multi-scale integration of diverse data types.
Occipital Neuralgia
Authors: Dellaria Andrea , Shah Nirav N. , Rubeiz Helene
Published: May 2018

According to the International Headache Society, occipital neuralgia is classified as a cranial neuralgia. It is characterized by paroxysmal pain in the distribution of the greater, lesser, or third occipital nerve. The pain is typically located in the upper posterior cervical region and radiates to the vertex of the scalp, and it may be reproduced upon palpation of the involved nerve. The diagnosis of occipital neuralgia can definitively be made if the patients achieves pain relief after a local anesthetic nerve block. Occipital neuralgia is often idiopathic, but secondary structural etiologies may be identified in some cases. Treatment options range from medical management to surgical intervention.
Trigeminal Neuralgia
Authors: Alshaikh Jumana T. , Sudhakaran Shaan , Rubeiz Helene
Published: May 2018

Trigeminal neuralgia is characterized by severe, unilateral, paroxysmal stabbing pain affecting the face in the distribution of one of the divisions of the trigeminal nerve. The episodes of pain are brief and are triggered by innocuous physical stimuli. Typical age of onset is the sixth decade, with a female predominance. The most common cause is neurovascular compression. Other causes include multiple sclerosis and structural abnormalities in the cerebellopontine angle. The diagnosis is made clinically, but MRI can be useful in evaluation of the underlying etiology. First-line pharmacotherapy is carbamazepine or oxcarbazepine. If medical therapy fails, procedural interventions should be considered. From ablations to craniotomy, there is an array of procedural treatments available for trigeminal neuralgia. Patients should be educated on the risks and benefits of each procedure prior to pursuing treatment.
Mechanical Chronic Jaw Pain
Authors: Grandhe Radhika P. , Valeriano Matthew , Souza Dmitri
Published: May 2018

Mechanical jaw pain and temporomandibular joint (TMJ) disorders are the most common causes of nondental orofacial pain. The pain can originate from the joint structures or from the muscles of mastication. Diagnosis is based predominantly on the clinical history and exam findings, but imaging is indicated in certain circumstances. Secondary causes of chronic jaw pain must be sought out and meticulously ruled out. Patients presenting with TMJ pain have a high prevalence of fibromyalgia and other chronic pain conditions. Multidisciplinary treatment involving medications, minimizing parafunctional habits, oral splints, physical therapy, psychotherapy, and injections forms the cornerstone of management of this complex condition. Surgery is indicated in select conditions, such as ankylosis of the joint or tumors.
Cervical Myofascial Pain
Authors: Wang Roger , Choxi Sarah
Published: May 2018

Cervical myofascial pain (CMP) is caused by trauma, spine pathology, repetitive strain, postural dysfunction, and physical deconditioning of the muscles that support the shoulders and neck. These include the trapezius, levator scapulae, splenius capitis, and rhomboid muscles. Treating the underlying etiology is the most effective therapy, however, it may be challenging to diagnose CMP, adding to the difficulty of definitive therapy. Management of CMP often requires a multidisciplinary approach incorporating physical therapy, pharmacotherapy, injection therapy, and behavioral modification. Neck pain is a common condition affecting two-thirds or more of the global population during their lifetime. The etiology of neck pain includes cervical disk disease, cervical facet-mediated pain, and CMP. In particular, CMP is often a cause of disability in the population with chronic neck pain.
Neurogenic Thoracic Outlet Syndrome
Authors: Stogicza Agnes , Singh Virtaj , Trescot Andrea
Published: May 2018

Neurogenic thoracic outlet syndrome (nTOS) is caused by compression of the brachial plexus as it travels from the exiting nerve roots to the axilla. Its presentation, with varying degrees and distributions of arm and hand pain, paresthesias, and numbness, is often either not recognized or is confused with other conditions. Delay in diagnosis causes ongoing suffering for patients, with a concomitant increased use of healthcare services. Imaging and electrodiagnostic studies are often unremarkable, and therefore the diagnosis is based on a detailed medical history, a thorough physical exam, and diagnostic injections. Treatment options are available and can lead to significantly improved quality of life for the patient. Increased awareness of nTOS will likely contribute to its proper diagnosis and treatment.
Chronic Knee Pain
Authors: Calisoff Randy L. , Walega David R.
Published: May 2018

Chronic knee pain affects 27 million people in the United States and is a leading cause of disability. Seventy percent of the population 65 years or older will have knee pain with radiographic evidence of osteoarthritis, and 12% will have clinical symptoms of osteoarthritis. Chronic knee pain after total knee replacement ranges from 10% to 20%. Patellofemoral pain syndrome (PFPS) refers to anterior knee pain exacerbated with knee joint loading activities (squatting, kneeling, prolonged sitting, ascending/descending stairs). PFPS is a clinical diagnosis, and treatment is directed toward pain alleviation and restoration of proper biomechanics. Pes anserine syndrome is common in runners, athletes, and individuals with osteoarthritis of the knee. Other risk factors include: female sex and a history of diabetes mellitus, obesity, or arthritis. Knowledge of the common knee pain etiologies, as well as key clinical manifestations, physical exam findings, differential diagnosis, and treatment options for each is important for pain specialists.
Complex Regional Pain Syndrome of the Upper and Lower Extremity
Authors: Stogicza Agnes , Tohotom Bartha Peter , Racz Edit , Trescot Andrea , Berkman Alan
Published: May 2018

Complex regional pain syndrome (CRPS) is a chronic debilitating pain condition of the extremities; it can affect, less commonly, other areas of the body (face, pelvis, abdomen). Its early presentation—pain disproportionate to the injury, skin temperature changes, hyperalgesia, allodynia—is often not recognized, delaying treatment. In later phases, with sympathetic nervous system involvement, it presents with skin and muscle atrophy, hair loss, allodynia, loss of function, and decreased range of motion. In severe cases, it can spread from one area to the other. Imaging findings (X-ray, MRI, bone scintigraphy) are nonspecific. They are used to support the diagnosis, and to exclude conditions that can present similarly. Treatment is challenging and includes physical therapy, psychologic support, medication management, and minimally invasive interventions to decrease pain, to positively influence the sympathetic nervous system, and to preserve function. A multidisciplinary approach is likely to be the most beneficial.
Phantom Limb Pain
Authors: Candido Kenneth D. , Kusper Teresa M. , Lissounov Alexei , Knezevic Nebojsa Nick
Published: May 2018

Post-amputation pain (PAP) has challenged clinicians for centuries. The first written record of this perplexing condition came from the 16th-century French military surgeon Ambrose Paré. The term phantom limb pain (PLP) was coined by Silas Weir Mitchell, who provided a comprehensive description of the condition during the 19th century. Since that time, the understanding of PLP has greatly expanded; however, our knowledge of the exact mechanisms underlying it is still very deficient. Amputation of a body part can result in one sequela or more than one neurologic sequelae occurring concurrently: phantom sensation, phantom pain, and stump pain. The incidence and prevalence vary across the spectrum of these syndromes. A myriad of treatment modalities are employed in an attempt to terminate PLP, including pharmacotherapy, injections, alternative therapy, surgical interventions, and neuromodulation. Despite an extensive search for effective therapeutic options, PLP remains a highly challenging and debilitating condition.
Postmastectomy Neuropathic Pain
Authors: Pranav Heena , Elmofty Dalia H.
Published: May 2018

Neuropathic pain can burden patients in multiple domains. It is a complex pain syndrome that remains difficult to treat. Detailed history and physical examination would reveal patients with neuropathic conditions complaining of burning, shocklike pain. There are a variety of neuropathic pain conditions that can be considered in a differential diagnosis. Because patients with neuropathic pain fail to obtain satisfactory relief from pharmacologic agents alone, a multidisciplinary approach that includes preventative and interventional options is recommended. Interventional treatment options may offer relief to patients with refractory neuropathic pain. Success in the treatment of neuropathic pain depends on evidence-based medicine and individualized patient care.
Chronic Abdominal Pain in the Elderly: Ischemic Pain
Authors: Reed Ashley , Malik Tariq M.
Published: May 2018

Elderly patients with chronic abdominal pain are commonly misdiagnosed, most likely due to atypical symptom presentations. Chronic mesenteric ischemia is a rare cause of chronic abdominal pain in the elderly. Symptoms are postprandial abdominal pain, weight loss, and an abdominal bruit. The disease results from atherosclerotic plaques that reduce the bowel’s ability to increase blood flow after meals. Patients often are malnourished. Diagnosis can be made with various imaging modalities, although a computed tomography angiogram is likely needed when the syndrome is suspected. The mainstay of therapy for chronic mesenteric ischemia is surgical intervention. Interventional pain techniques, such as celiac plexus neurolysis or spinal cord stimulation, are promising adjunct treatment options.
Chronic Pelvic Pain
Authors: Rastogi Rahul , Kamal Saima , Garg Shuchita
Published: May 2018

Chronic pelvic pain (CPP) is defined as nonmalignant pain in lower abdominal and pelvic structures that has persisted for more than 6 months. Although CPP mostly occurs in women, it can also affect men. In the United States, the prevalence of CPP in women age 18 to 50 is estimated to be 1 in 7. In the United Kingdom, the annual prevalence of CPP in primary care settings is around 3.8% in women age 15 to 73 years. About 10% of referrals to gynecologists are for pelvic pain; 20% of the referrals undergo hysterectomies and 40% undergo laparoscopic surgeries. The pain can be somatic, visceral, or neurogenic, making the differential diagnosis challenging. A detailed, comprehensive evaluation is necessary to diagnose CPP. Often, even after a thorough evaluation, the etiology remains unclear. Multisystem involvement requires specialist referral. CPP can be psychologically and physically debilitating, and, along with disease-specific treatments, often requires a multidisciplinary approach for optimal pain management.
Postlaminectomy Syndrome
Authors: Candido Kenneth D. , Tverdohleb Tatiana , Knezevic Nebojsa Nick
Published: May 2018

Postlaminectomy syndrome is persistent or recurrent back pain after otherwise anatomically successful lumbar spine surgery. A dramatic increase in the number of low back surgeries has been observed since 1997, with an increased incidence of pain after low back surgery in the range of 5% to 74.6%. The mechanisms contributing to back pain are muscle damage during surgery, muscle spasm, and inflammation, with subsequent development of myofascial pain syndrome as well as other typical and atypical back pain generators. Diagnosis is based primarily on history and physical examination, as well as results of imaging (preoperative and postoperative). Treating postlaminectomy syndrome is challenging, due to lack of evidence-based clinical guidelines. Pharmacologic treatment in combination with interventional management sometimes is not enough, and choosing the right candidates for revision and reoperation surgery is mainly based on the surgeon’s experience and best clinical judgment. In certain circumstances, spinal cord stimulation can achieve better results than reoperation.
Malignant Visceral Pain
Authors: Wolf James , Pino Carlos A.
Published: May 2018

Healthcare providers are familiar with the diffuse and poorly localized quality of visceral pain, as well as its somatic referral patterns from internal organs to dermatomal distributions. Visceral pain also involves significant autonomic and emotional components. When primary or metastatic malignancy is responsible for visceral pain, treating the patient’s pathology and symptomatology becomes more complex. Visceral pain can be initiated by distension of hollow organs, mesenteric traction, ischemia, and inflammatory factors, all of which are associated with solid tumors in the abdomen. Furthermore, common analgesics, such as opioids, can negatively affect visceral function, leading to nausea, vomiting, or constipation, which may negate the drugs’ beneficial effects or even worsen pathology and pain. While clinicians have tools to alleviate visceral pain, none has a perfect efficacy or side effect profile. In metastatic disease, the focus of care should be on improvement of a patient’s quality of life based on his or her personal goals and expectations.
Intrathecal Drug Delivery Systems
Authors: Agarwal Deepti , Ifeanyi Ifeyinwa C. , Udoji Mercy A.
Published: May 2018

Intrathecal drug delivery (ITDD), while initially intended for terminal oncology patients suffering from cancer pain, is currently widely used for chronic nonmalignant pain states. Before intrathecal drug delivery device (IDDD) implantation, patients with nonmalignant chronic pain must be screened for psychologic, behavioral, and medical etiologies for their pain, in addition to having a documented failure of maximal medical therapy and a successful intrathecal drug trial. Classes of drugs used for intrathecal therapy include opioids, local anesthetics, adrenergic agonists, and NMDA receptor agonists. Drugs currently approved by the FDA for ITDD are morphine, ziconotide, and baclofen. Complications of IDDD implantation are surgical (bleeding, infection, CSF leak, nerve injury), mechanical (due to catheter kink, shear, or disconnection), pharmacologic (overdose, incorrect pump settings, contaminated drugs), or medical (hypogonadotropic hypogonadism).
Ketamine Use and Opioid-Tolerant Cancer Patients
Authors: Yousefshahi Fardin , Michelagnoli Giuliano , Asenjo Juan Francisco
Published: May 2018

Pain occurs in up to 70% of cancer patients and it can be challenging to manage. The standard for analgesic therapy is the World Health Organization ladder; however, up to 25% of patients don’t reach a level of comfort using this approach. Ketamine has been recognized as an excellent adjuvant for cancer pain treatment, especially when other analgesics have failed. Some randomized clinical trials have confirmed ketamine’s efficacy in refractory cancer pain, but most had small sample sizes and low power. Some publications have confirmed the beneficial effect of oral, intranasal, subcutaneous, or intravenous ketamine in treatment of refractory chronic cancer pain, while others are less conclusive. While ketamine is rapidly gaining ground as an adjuvant in treating pain in patients with cancers refractory to conventional therapy and/or patients with opioid tolerance, care should be taken to identify patients with ketamine contraindications in order to offer the greatest benefit with the lowest risk of side effects.
Psychiatric Comorbidities in Chronic Pain Syndromes
Authors: Beckman Nancy J. , Tobin Marie B.
Published: May 2018

Psychiatric comorbidities are common in patients with chronic pain syndromes. Depression, anxiety, insomnia, somatic symptom disorder, substance use disorders, personality disorders, and problematic coping strategies present unique treatment challenges to pain medicine specialists. Patients with these comorbidities tend to have poorer response to treatment, higher rates of complications, and greater pain-related suffering. To reduce stigma, providers are encouraged to define pain as both a sensory and emotional experience. This intimate connection implies that optimal pain treatment requires concurrent attention to psychosocial well-being. Overlapping biological and psychologic mechanisms in the development of chronic pain and psychiatric disorders may contribute to the high rates of comorbidity. Methods for quickly identifying psychiatric disorders within busy clinic settings and brief interventions that pain specialists can deliver are described. Finally, indications for referral to specialty mental health and the benefits of multidisciplinary treatment, which can include psychiatric medications and evidence-based psychologic treatments, such as cognitive-behavioral therapy, are discussed.