Global Relaxation Research Articles

Longitudinal evaluation of T1ρ and T2 spatial distribution in osteoarthritic and healthy medial knee cartilage

To investigate longitudinal changes in laminar and spatial distribution of knee articular cartilage magnetic resonance imaging (MRI) T1ρ and T2 relaxation times, in individuals with and without medial compartment cartilage defects. All subjects (at baseline n=88, >18 years old) underwent 3-Tesla knee MRI at baseline and annually thereafter for 3 years. The MR studies were evaluated for presence of cartilage defects (modified Whole-Organ Magnetic Resonance Imaging Scoring - mWORMS), and quantitative T1ρ and T2 relaxation time maps. Subjects were segregated into those with (mWORMS ≥2) and without (mWORMS ≤1) cartilage lesions at the medial tibia (MT) or medial femur (MF) at each time point. Laminar (bone and articular layer) and spatial (gray level co-occurrence matrix - GLCM) distribution of the T1ρ and T2 relaxation time maps were calculated. Linear regression models (cross-sectional) and Generalized Estimating Equations (GEEs) (longitudinal) were used. Global T1ρ, global T2 and articular layer T2 relaxation times at the MF, and global and articular layer T2 relaxation times at the MT, were higher in subjects with cartilage lesions compared to those without lesions. At the MT global T1ρ relaxation times were higher at each time point in subjects with lesions. MT T1ρ and T2 became progressively more heterogeneous than control compartments over the course of the study. Spatial distribution of T1ρ and T2 relaxation time maps in medial knee OA using GLCM technique may be a sensitive indicator of cartilage deterioration, in addition to whole-compartment relaxation time data.

Quadriceps and Hamstrings Morphology Is Related to Walking Mechanics and Knee Cartilage MRI Relaxation Times in Young Adults

Controlled laboratory study using a cross-sectional design. To analyze the relationship of quadriceps-hamstrings and medial-lateral quadriceps anatomical cross-sectional area (ACSA) ratios with knee loads during walking and articular and meniscal cartilage composition in young, healthy subjects. Muscle forces affect knee loading during walking, but it is not known if muscle morphology is associated with walking mechanics and cartilage composition in young subjects. Forty-two knees from 27 young, healthy, active volunteers (age, 20-35 years; body mass index, <28 kg/m(2)) underwent 3-T magnetic resonance imaging (MRI) and 3-D motion capture. Standard MRI sequences were used for articular and meniscal cartilage T1rho and T2 relaxation times and for quadriceps and hamstrings muscle ACSA. Frontal plane kinetics during the stance phase of walking was calculated. Generalized estimating equation models were used to identify muscle variables that predicted MRI and gait parameters. Quadriceps-hamstrings and medial-lateral quadriceps ACSA ratios were positively related to frontal plane loading (β = .21-.54, P≤.006), global articular cartilage relaxation times (β = .22-.28, P≤.041), and the medial-lateral ratio of meniscus T1rho relaxation time (β = .26-.36, P≤.049). The medial-lateral quadriceps ACSA ratio was positively related to global meniscus T1rho relaxation times (β = .30, P = .046). Higher quadriceps-hamstrings and medial-lateral quadriceps ACSA ratios were associated with higher frontal plane loading during walking and with articular and meniscal cartilage T1rho and T2 relaxation times. These findings highlight the relationships between different knee tissues and knee mechanics in young, healthy individuals.

POS-SUPPORTED AUTOMATIC DIGITAL SURFACE MODEL (DSM) GENERATION

Abstract. A novel method of POS supported dense matching is introduced for automatically generating DSM. The image pre-processing includes adaptive smooth filter and Wallis filter. The method based on the correlation coefficient with geometric constraint, POS supported geometry corrective for matching window, and global relaxation optimization is introduced in the process of matching for determining the homogeneous points. The Multi-image space intersection method with outlier elimination function is used to realize the matching result to integrate into the object space and generate coarse DSM. The matching results of upper pyramid generating a coarse DSM, which is used to constrain and guide the subsequent pyramid image matching, until the original image. Finally, the feasibility of the method proposed in this paper is verified by the experiments, which tests on different scales of aerial images.

Cardiovascular effects of 3 months of football training in overweight children examined by comprehensive echocardiography: a pilot study

We examined effects of a 3-month football training programme in overweight children using comprehensive echocardiography and peripheral arterial tonometry. Twenty preadolescent overweight children (17 boys, 3 girls aged 8–12 yrs; body mass index [BMI] ≥ 85th percentile) participated in a structured 3-month football training programme, consisting of 4 weekly 60–90 min sessions with mean heart rate (HR) > 80% of HRmax (football group, FG). A parallel control group (CG) included 11 children (7 boys, 4 girls) of equivalent age from an obesity clinic. After 3 months, systolic blood pressure was unchanged in FG, but had increased in CG (112 [s 6] vs. 122 [10] mmHg, P = 0.02). FG demonstrated increased left ventricular (LV) posterior wall diameter (0.60 [0.07] vs. 0.68 [0.10] cm, P < 0.001) and an improved right ventricular systolic function determined by tricuspid annular plane systolic excursion (TAPSE, 2.01 [0.29] vs. 2.27 [0.28] cm, P = 0.003). Measures of LV systolic function showed only discrete alterations and two-dimensional (2D) global strain was not changed. After 3 months, global isovolumetric relaxation time (IVRTglobal) had increased in FG (64.0 [7.5] vs. 73.9 [9.4] ms, P < 0.001) while other examined LV diastolic function variables were not altered. No echocardiographic changes were observed in CG. Between-group differences in pre-post delta values were observed for systolic blood pressure, TAPSE, and IVRTglobal (P = 0.02–0.03). We conclude that short-term football training may have positive structural and functional effects on the cardiovascular system in overweight preadolescent children.

Early diastolic strain rate in relation to systolic and diastolic function and prognosis in acute myocardial infarction: a two-dimensional speckle-tracking study

Diastolic dysfunction in acute myocardial infarction (MI) is associated with adverse outcome. Recently, the ratio of early mitral inflow velocity (E) to global diastolic strain rate (e'sr) has been proposed as a marker of elevated LV filling pressure. However, the prognostic value of this measure has not been demonstrated in a large-scale setting when existing parameters of diastolic function are known. We hypothesized that the E/e'sr ratio would be independently associated with an adverse outcome in patients with MI. We prospectively included patients with MI and performed echocardiography with comprehensive diastolic evaluation including E/e'sr. The relationship between E/e'sr and the primary composite endpoint (all-cause mortality, hospitalization for heart failure (HF), stroke, and new onset atrial fibrillation) was analysed with Cox models. A total of 1048 patients (mean age 63 ± 12, 73% male) were included and 142 patients (13.5%) reached the primary endpoint (median follow-up 29 months). A significant prognostic value was found for E/e'sr [hazard ratio (HR) per 1 unit change: 2.36, 95% confidence interval (CI): 2.02-2.75, P < 0.0001]. After multivariable adjustment E/e'sr remained independently related to the combined endpoint (HR per 1 unit change, 1.50; CI: 1.05-2.13, P = 0.02). The prognostic value of E/e'sr was driven by mortality (HR per 1 unit change, 2.52; CI: 2.09-3.04, P < 0.0001) and HF admissions (HR per 1 unit change, 2.79; CI: 2.23-3.48, P < 0.0001). Deformation-based E/e'sr contributes important information about global myocardial relaxation superior to velocity-based analysis and is independently associated with the outcome in acute MI.

Subpicosecond processes in nucleic acids bases monitored by Raman spectroscopy

In this work the Raman total half band widths of five nucleic acids nitrogenous bases (adenine, guanine, cytosine, thymine and uracil) have been measured, respectively. Raman scattering can be used to study the fast subpicosecond dynamics of purinic and pyrimidinic nucleic acids bases in solid state. The dependencies of the total half band widths and of the corresponding global relaxation times, on atomic groups and on the type of free nucleic acids bases, are reported. In our study, the full widths at half-maximum (FWHMs) for the Raman bands of nucleic acids bases, are typically in the wavenumber range from 9.5 to 22 cm−1. Besides, it can be observed that molecular relaxation processes studied in this work, have a global relaxation time value smaller than 1.06 ps and larger than 0.46 ps. We have found that the band centered at 941 cm−1 of adenine, the profiles near 1232 cm−1, 1678 cm−1, in the case of guanine, the band around 1116 cm−1 attributed to cytosine, the profiles at 1490, 1673 cm−1 attributed to thymine and several Raman bands corresponding to atomic groups in uracil, respectively, are suitable for further studying the dynamical behavior of molecular fragments in nucleic acids bases.

Iterative Method for Edge Length Equalization

This paper presents a method for triangular surface remeshing to obtain new faces whose edge lengths are as close as possible to a target value m. The process uses as input a 2-manifold mesh with arbitrary geometry and topology. The proposed algorithm runs iteratively, automatically adjusting the necessary amount of vertices, and applies a global relaxation process using a variation of Laplace-Beltrami discrete operator. We introduce geometry constraints in order to preserve salient features of the original model. The method results on a grid with edge lengths near to m with low standard deviation, i.e. the vertices are uniformly distributed over the original surface. The dual space of the final triangular surface results in a trivalent, mostly hexagonal mesh, suitable for several applications.

Efficient Relaxation of Protein-Protein Interfaces by Discrete Molecular Dynamics Simulations.

Protein-protein interactions are responsible for the transfer of information inside the cell and represent one of the most interesting research fields in structural biology. Unfortunately, after decades of intense research, experimental approaches still have difficulties in providing 3D structures for the hundreds of thousands of interactions formed between the different proteins in a living organism. The use of theoretical approaches like docking aims to complement experimental efforts to represent the structure of the protein interactome. However, we cannot ignore that current methods have limitations due to problems of sampling of the protein-protein conformational space and the lack of accuracy of available force fields. Cases that are especially difficult for prediction are those in which complex formation implies a non-negligible change in the conformation of the interacting proteins, i.e., those cases where protein flexibility plays a key role in protein-protein docking. In this work, we present a new approach to treat flexibility in docking by global structural relaxation based on ultrafast discrete molecular dynamics. On a standard benchmark of protein complexes, the method provides a general improvement over the results obtained by rigid docking. The method is especially efficient in cases with large conformational changes upon binding, in which structure relaxation with discrete molecular dynamics leads to a predictive success rate double that obtained with state-of-the-art rigid-body docking.

Cardiac Dysfunction and Prolonged Hemodynamic Deterioration After Implantable Cardioverter-Defibrillator Shock in Patients With Systolic Heart Failure

We investigated the acute effects of implantable cardioverter-defibrillator shock on myocardium, cardiac function, and hemodynamics in relation to left ventricular systolic function. We studied 50 patients who underwent implantable cardioverter-defibrillator implantation and defibrillation threshold (DFT) testing: 25 patients with left ventricular ejection fraction (LVEF) ≥ 45% and 25 patients with LVEF <45%. We measured cardiac biomarkers (creatine kinase, creatine kinase-MB, myoglobin, cardiac troponin T and I, and N-terminal probrain natriuretic peptide). Left ventricular relaxation was assessed by global longitudinal strain rate during the isovolumetric relaxation period using speckle-tracking echocardiography. Blood sampling and echocardiography were performed before, immediately after, and 5 minutes and 4 hours after DFT testing. Mean arterial pressure was measured directly during DFT testing. Cardiac biomarkers showed no significant changes in either group. LVEF was decreased until 5 minutes after DFT testing and had recovered to the baseline at 4 hours in the group with reduced LVEF (P<0.001), whereas LVEF reduction was not observed in the group with preserved LVEF (P=0.637). Global isovolumetric relaxation period was decreased until 5 minutes after DFT testing and had recovered to the baseline at 4 hours in both groups (preserved LVEF: 0.39 ± 0.14 versus 0.23 ± 0.13* versus 0.23 ± 0.13* versus 0.40 ± 0.13 s(-1), *P<0.001 versus baseline; reduced LVEF: 0.15 ± 0.05 versus 0.08 ± 0.04† versus 0.09 ± 0.04† versus 0.15 ± 0.05 s(-1), †P<0.001 versus baseline, repeated-measures ANOVA). Time to recovery of mean arterial pressure to the baseline was prolonged in the group with reduced LVEF (P<0.001). Implantable cardioverter-defibrillator shock transiently impairs cardiac function and hemodynamics especially in patients with systolic dysfunction, although significant tissue injury is not observed.

Field- and time-dependent, local and global magnetization behaviour of out-of-plane textured SmCo5 thin films

This work presents an investigation of the magnetization processes in out-of-plane textured SmCo5 thin films by means of domain observations with magnetic force microscopy (MFM). Starting from the thermally demagnetized state, an applied field was increased stepwise until saturation, and the magnetic domain pattern was recorded at the respective field. Additionally, the change in the domain structure was investigated for the demagnetization branch to observe the full reversal process from positive to negative saturation. In a second experiment, various opposite fields were applied to the film after previous saturation and the time-dependent domain evolution was measured. The directly observed domain behaviour specifies the influence of pinning and nucleation on the magnetizing and demagnetizing process.From these time-dependent domain images, magnetization curves were constructed and the resulting viscosity is compared with data from global magnetization measurements. The viscosity as determined from MFM data is measurably larger than that deduced from global relaxation measurements, which demonstrates the influence of the tip's magnetization on the reversal mechanism.

Thermal relaxation for the Relativistic Ornstein–Uhlenbeck Process

The thermal relaxation of a relativistic particle diffusing in a fluid at equilibrium is investigated through a numerical study of the Relativistic Ornstein–Uhlenbeck Process. The spectrum of the relaxation operator has both a discrete and a continuous component. Both components are fully characterized and the limit between them is given a simple interpretation. Short-time relaxation is addressed separately, and a global effective relaxation time is also computed. The general conclusion is that relativistic effects slow down thermalization.

Relaxation creep rupture of heterogeneous material under constant strain

We focus on a system consisting of an elastic part and a damageable part in series, to study the relaxation creep rupture of a heterogeneous system subjected to a uniaxial constant strain applied instantaneously. The viscoelastic behavior of the damageable part is modeled by a fiber bundle model consisting of Kelvin-Voigt elements and global load sharing is assumed for the redistribution of load following fiber breaking in the damageable part. Analytical and numerical calculations show that the global relaxation creep rupture appears if the elastic energy stored in the elastic part exceeded the fracture energy of the damageable part. The lifetime of the system strongly depends on the values of the applied external strain and the initial stiffness ratio k between the elastic part and the damageable part. We show that a higher stiffness ratio implies a more brittle system. Prior to complete failure, relaxation creep rupture exhibits a sequence of three stages, similar to creep rupture under constant stress, and the nominal force rate presents a power law singularity with a power index -1/2 near the global rupture time.

Localized relaxation theory of circuits and its applications in electro-thermal analyses

In the high-performance IC design with increasing design complexity, it is a very important design content to efficiently analyze IC parameters. Thus, the electro-thermal (ET) analyses including power/ground (P/G) analysis and thermal analysis are hot topics in today’s IC research. Since ET analysis equation has a sparse, positive definite and strictly diagonally dominant coefficient-matrix, we prove that the ET analysis has the advantage of locality. Owing to this advantage, localized relaxation method is formally proposed, which has the same accuracy as the global relaxation done with the constraint of the same truncation error limitation. Based on the localized relaxation theory, an efficient and practical localized successive over-relaxation algorithm (LSOR2) is introduced and applied to solve the following three ET analysis problems. (1) Single-node statistical voltage analysis for over-IR-drop nodes in P/G networks; (2) single-node statistical temperature analysis for hot spots in 3D thermal analysis; (3) fast single open-defect analysis for P/G networks. A large amount of experimental data demonstrates that compared with the global successive over-relaxation (SOR) algorithm, LSOR2 can speed up 1–2 orders of magnitudes with the same accuracy in ET analyses.

Spatio-temporal attributes of left ventricular pressure decay rate during isovolumic relaxation

Global left ventricular (LV) isovolumic relaxation rate has been characterized: 1) via the time constant of isovolumic relaxation τ or 2) via the logistic time constant τ(L). An alternate kinematic method, characterizes isovolumic relaxation (IVR) in accordance with Newton's Second Law. The model's parameters, stiffness E(k), and damping/relaxation μ result from best fit of model-predicted pressure to in vivo data. All three models (exponential, logistic, and kinematic) characterize global relaxation in terms of pressure decay rates. However, IVR is inhomogeneous and anisotropic. Apical and basal LV wall segments untwist at different times and rates, and transmural strain and strain rates differ due to the helically variable pitch of myocytes and sheets. Accordingly, we hypothesized that the exponential model (τ) or kinematic model (μ and E(k)) parameters will elucidate the spatiotemporal variation of IVR rate. Left ventricular pressures in 20 subjects were recorded using a high-fidelity, multipressure transducer (3 cm apart) catheter. Simultaneous, dual-channel pressure data was plotted in the pressure phase-plane (dP/dt vs. P) and τ, μ, and E(k) were computed in 1631 beats (average: 82 beats per subject). Tau differed significantly between the two channels (P < 0.05) in 16 of 20 subjects, whereas μ and E(k) differed significantly (P < 0.05) in all 20 subjects. These results show that quantifying the relaxation rate from data recorded at a single location has limitations. Moreover, kinematic model based analysis allows characterization of restoring (recoil) forces and resistive (crossbridge uncoupling) forces during IVR and their spatio-temporal dependence, thereby elucidating the relative roles of stiffness vs. relaxation as IVR rate determinants.

QM/MM Reweighting Free Energy SCF for Geometry Optimization on Extensive Free Energy Surface of Enzymatic Reaction.

We developed a quantum mechanical/molecular mechanical (QM/MM) free energy geometry optimization method by which the geometry of a quantum chemically treated (QM) molecule is optimized on a free energy surface defined with thermal distribution of the surrounding molecular environment obtained by molecular dynamics simulation with a molecular mechanics (MM) force field. The method called QM/MM reweighting free energy self-consistent field combines a mean field theory of QM/MM free energy geometry optimization developed by Yamamoto (Yamamoto, T. J. Chem. Phys.2008, 129, 244104) with a reweighting scheme for updating the MM distribution introduced by Hu et al. (Hu, H., et al. J. Chem. Phys.2008, 128, 034105) and features high computational efficiency suitable for exploring the reaction free energy surface of extensive protein conformational space. The computational efficiency with improved treatment of a long-range electrostatic (ES) interaction using the Ewald summation technique permits one to take into account global conformational relaxation of an entire protein of an enzyme in the free energy geometry optimization of its reaction center. We applied the method to an enzymatic reaction of a substrate complex of psychrophilic α-amylase from Antarctic bacterium Pseudoalteromonas haloplanktis and succeeded in geometry optimizations of the reactant and the product of the catalytic reaction that involve large conformational changes of protein loops adjacent to the reaction center on time scales reaching sub-microseconds. We found that the adjacent loops in the reactant and the product form in different conformations and produce catalytic ES potentials on the reaction center.

Aging Through Hierarchical Coalescence in the East Model

We rigorously analyze the low temperature non-equilibrium dynamics of the East model, a special example of a one dimensional oriented kinetically constrained particle model, when the initial distribution is different from the reversible one and for times much smaller than the global relaxation time. This setting has been intensively studied in the physics literature to analyze the slow dynamics which follows a sudden quench from the liquid to the glass phase. In the limit of zero temperature (i.e. a vanishing density of vacancies) and for initial distributions such that the vacancies form a renewal process we prove that the density of vacancies, the persistence function and the two-time autocorrelation function behave as staircase functions with several plateaux. Furthermore the two-time autocorrelation function displays an aging behavior. We also provide a sharp description of the statistics of the domain length as a function of time, a domain being the interval between two consecutive vacancies. When the initial renewal process has finite mean our results confirm (and generalize) previous findings of the physicists for the restricted case of a product Bernoulli measure. However we show that a different behavior appears when the initial domain distribution is in the attraction domain of a $\alpha$-stable law. All the above results actually follow from a more general result which says that the low temperature dynamics of the East model is very well described by that of a certain hierarchical coalescence process, a probabilistic object which can be viewed as a hierarchical sequence of suitably linked coalescence processes and whose asymptotic behavior has been recently studied in [14].

局部松弛电路理论及其在电热分析中的应用

In the high-performance IC design with increasing design complexity, it is a very important design con- tent to efficiently analyze IC parameters. Thus, the electro-thermal(ET) analyses including power/ground(P/G) analysis and thermal analysis are hot topics in today's IC research. Since ET analysis equation has a sparse, positive definite and strictly diagonally dominant coefficient-matrix, we prove that the ET analysis has the ad- vantage of locality. Owing to this advantage, localized relaxation method is formally proposed, which has the same accuracy as the global relaxation done with the constraint of the same truncation error limitation. Based on the localized relaxation theory, an efficient and practical localized successive over-relaxation algorithm(LSOR2) is introduced and applied to solve the following three ET analysis problems: (1) Single-node statistical voltage analysis for over-IR-drop nodes in P/G networks; (2) single-node statistical temperature analysis for hot spots in 3D thermal analysis; (3) fast single open-defect analysis for P/G networks. A large amount of experimental data demonstrates that compared with the global successive over-relaxation(SOR) algorithm, LSOR2 can speed up 1-2 orders of magnitudes with the same accuracy in ET analyses.

Inherent Si dangling bond defects at the thermal (110)Si/SiO2interface

Stimulated by the growing manifestation in advanced semiconductor device development, an extensive multifrequency electron spin resonance (ESR) study has been carried out on the thermal (110)Si/SiO${}_{2}$ interface in terms of occurring paramagnetic point defects as a function of oxidation temperature ${T}_{\mathit{ox}}$ (200--1125 \ifmmode^\circ\else\textdegree\fi{}C), with seclusion of the H-passivation factor. The main type of defect observed is a P${}_{\mathrm{b}}$-type interface center closely related to the P${}_{\mathrm{b}}$${}^{(111)}$ and P${}_{\mathrm{b}0}$${}^{(100)}$ variants (Si${}_{3}$ \ensuremath{\equiv} Si${}^{\ifmmode\bullet\else\textbullet\fi{}}$) characteristic for the (111) and (100)Si faces, respectively. The inferred principal g matrix values (${g}_{//}$ = 2.0018 and ${g}_{\ensuremath{\perp}}$ = 2.0082 for ${T}_{\mathit{ox}}$ = 800 \ifmmode^\circ\else\textdegree\fi{}C), splitting parameters of the resolved ${}^{29}$Si hyperfine doublet, and line width behavior closely resemble those of P${}_{\mathrm{b}0}$${}^{(100)}$, from which the defect is typified as P${}_{\mathrm{b}0}$${}^{(110)}$. For low ${T}_{\mathit{ox}}$, an unexpectedly high density of P${}_{\mathrm{b}0}$${}^{(110)}$ defects (\ensuremath{\sim}7 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$) is observed, which gradually dwindles for ${T}_{\mathit{ox}}$ increasing above \ensuremath{\sim}700 \ifmmode^\circ\else\textdegree\fi{}C to approach \ensuremath{\sim}4 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$ for ${T}_{\mathit{ox}}$ \ensuremath{\rightarrow} 1125 \ifmmode^\circ\else\textdegree\fi{}C. The behavior is related to interfacial stress release as a result of global structural relaxation of the top SiO${}_{2}$ layer, an effect also signaled by attendant alterations in ESR parameters, including a drop in ESR line width and a change in line shape symmetry and ${g}_{\ensuremath{\perp}}$. Comparison with previous ESR data on (111)Si/SiO${}_{2}$ and (100)Si/SiO${}_{2}$ interfaces indicates that, in terms of P${}_{\mathrm{b}}$ type, the (110) face is the worst of all three low-index Si interfaces, i.e., [P${}_{\mathrm{b}0}$${}^{(100)}$] [P${}_{\mathrm{b}}$${}^{(111)}$] [P${}_{\mathrm{b}0}$${}^{(110)}$], in contrast with the common electrically inferred interface trap density order; only for ${T}_{\mathit{ox}}$ \ensuremath{\geqslant} 900 \ifmmode^\circ\else\textdegree\fi{}C does the (110) face slightly improve on the (111)Si one, raising caution with the application of (110)Si/SiO${}_{2}$ in terms of vulnerability during device operation. The comparison further shows that, unlike a textbook quote, the density of occurring P${}_{\mathrm{b}(0)}$ centers is not found to be proportional to Si surface areal atom density or available Si bond density. Instead, an empirically inferred matching criterion appears to be the surface areal Si atom density scaled by the number of bonds per atom directed into the oxide. Besides P${}_{\mathrm{b}0}$${}^{(110)}$, an apparently isotropic second type of interface center is revealed, baptized ${I}_{\mathrm{x}}$, at $g$ = 2.0048 with a density of \ensuremath{\sim}1 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$ that is rather independent of ${T}_{\mathit{ox}}$. Showing a similar passivation behavior in H${}_{2}$ as the P${}_{\mathrm{b}0}$${}^{(110)}$ center, it is also interpreted as a Si dangling-bond-type defect, now residing in an interfacial randomized Si environment---a variant of the D center.

Inherent interfacial Si dangling bond point defects in thermal (1 1 0)Si/SiO 2

A low-temperature electron spin resonance (ESR) study has been carried out on thermal (1 1 0)Si/SiO 2 as a function of oxidation temperature T ox with the intend to evaluate on atomic level the interface nature in terms of occurring inherent point defects which are at the origin of technologically detrimental traps. This reveals a remarkably high density of P b-type interface centers (interfacial Si dangling bonds), which variant, based on coinciding ESR parameters, is typified as P b0 (110), close to P b0 (100) at the (1 0 0)Si/SiO 2 interface. Starting at 7.5 × 10 12 cm −2, from T ox ≈ 700 °C onward, the density [P b0 (110)] gradually decreases by about 50% for T ox → 1100 °C – a result of global structural relaxation of the top SiO 2 layer as exposed by several ESR parameters. In terms of P b(0) centers, the (1 1 0) face is found to be the worst of all three low-index Si interfaces, i.e., [P b0 (100)] < [P b (111)] < [P b0 (110)], over the range T ox < ∼900 °C. For T ox ⩾ 900 °C, the (1 1 0)Si face does slightly improve over the (1 1 1)Si one, herewith underlining the importance of T ox not only for such comparative defect studies but also for interface optimization.

Commentary on Haberstick et al. (2011): Dizziness upon initial experimentation with cigarettes – implications for smoking persistence

Haberstick and colleagues [1], in a study published elsewhere in this issue, utilized a genetically informative same- and opposite-sex twin and sibling sample involving 2482 subjects in an attempt to tease out environmental and heritable differences in susceptibility for smoking and nicotine dependence. The focus was upon subjective responses to initial exposure to tobacco smoke using the Early Smoking Experiences (ESE) questionnaire [2,3], a nine-item self-report instrument that asks participants to rate retrospectively the following responses: global pleasant sensations, global unpleasant sensations, nausea, relaxation, dizziness, buzz/rush, coughing, difficulty inhaling and heart pounding. Responses were dichotomized as present or absent. The authors found that pleasant and unpleasant sensations demonstrated high internal reliability. Further, effects rated as pleasant were associated with greater likelihood of regular smoking, whereas those rated as unpleasant were associated with inconsistent use of cigarettes or not smoking. The overall findings of this well controlled and carefully executed study support and strengthen prior research on early smoking experiences. Hereditability of positive experiences, negative experiences and dizziness was 35%, 18% and 31%, respectively. Multivariate genetic modeling by the authors revealed an underlying factor with 37% hereditability that loaded strongly with reports of dizziness at the first cigarette. The identification of dizziness as a gateway variable that serves as a common pathway to regular cigarette smoking is an important finding as a precursor for further exploration of genetic mechanisms in smoking and more precise delineation of genetic differences between smokers and non-smokers. In our initial reports on the ESE [2,3], while dizziness differentiated smokers from never-smokers and was seldom reported by people who did not go on to become smokers, the sensation seemed to be affectively neutral. In subsequent studies using more sophisticated analytical techniques, however, dizziness emerged as a latent factor that correlated with both pleasant and unpleasant sensations [4]—a finding replicated in the study by Haberstick and colleagues. The distinction between ‘pleasant dizziness’ and ‘unpleasant dizziness’[5] and the contribution of affective valence to the continuation of smoking clearly deserves further investigation. Haberstick and colleagues were able to rule out sex differences in the affective valence of dizziness. A complication not addressed, however, is the possibility that the enjoyment of dizziness may, like novelty-seeking, decline with age—a shortcoming of retrospective assessment that may be relevant. Retrospective reports of dizziness upon initial experimentation have been shown to serve as good predictors of response to the administration of nicotine nasal spray [6]. Studies of life-span variability in the affective valence of dizziness, and the possible effect of other person variables as well, should enhance the utility of this measure. An additional potential threat to validity in earlier studies—including our own—is the failure to provide participants with a precise definition of the term ‘dizziness’. Roget's online thesaurus [7] offers a list of synonyms that includes some that few people would find pleasant (e.g. ‘vertigo’, ‘wooziness’) but others that many might endorse as positive (e.g. ‘giddiness’, ‘lightheadedness’). Future research on dizziness and smoking will be well-served by efforts to refine the item-set to ensure that all participants are ‘on the same page’. Overall, Haberstick and colleagues have made a very good start towards the disentangling of key issues. Continued refinement of the variables involved will certainly contribute to a better understanding of the mechanisms underlying the development of regular smoking and nicotine dependence—and possibly of other types of substance use as well [8]. None. The authors' research on early smoking experimentation was funded by National Institutes of Health Grants DA017640 and DA006529.