Summary Indices such as smoothness, movement time, peak velocity, and symmetry of the velocity profile have been shown to be effective in explaining the degree of skilfulness of human saccadic eye, ...limb, and jaw motions. We investigated whether adult subjects with mandibular prognathism show impaired smoothness of the masticatory jaw movements. Forty‐nine adults with skeletal Class III malocclusions and 52 healthy adults with acceptably good occlusions were selected respectively as Test and Control subjects. Subjects of the Test Group were subdivided into two groups: Class IIIclosed showed full occlusal contact between the upper and lower teeth at the habitual intercuspal position, whereas Class IIIopen showed inability of occlusal contact between the upper and lower anterior teeth. Each subject was asked to chew a piece of chewing gum. The normalised jerk‐cost (NJC), movement duration, and tangential velocity profile during jaw‐closing movements were compared between groups. Test Groups showed greater NJC (P < 0·01) with longer movement duration (P < 0·01) and lower peak velocity (P < 0·01) than the Control Group did. Class IIIclosed showed greater NJC (P < 0·01) with longer movement duration (P < 0·01) and lower peak velocity (P < 0·01) than Class IIIopen did. Results show that the mandibular movements made by the Test Groups exhibit lower skilfulness than those made by the Control Group. The jaw movement skilfulness of the prognathic patients decreases most drastically with existence of malocclusal contact between upper and lower anterior teeth.
The oxygen nonstoichiometry of La0.6Sr0.4CoO3−δ has been the topic of various reports in the literature, but has been exclusively measured at high oxygen partial pressures, pO2, and/or elevated ...temperatures. For applications of La0.6Sr0.4CoO3−δ, such as solid oxide fuel cell cathodes or oxygen permeation membranes, knowledge of the oxygen nonstoichiometry and thermo-chemical stability over a wide range of pO2 is crucial, as localized low pO2 could trigger failure of the material and device. By employing coulometric titration combined with thermogravimetry, the oxygen nonstoichiometry of La0.6Sr0.4CoO3−δ was measured at high and intermediate pO2 until the material decomposed (at log(pO2/bar)≈−4.5 at 1073K). For a gradually reduced sample, an offset in oxygen content suggests that La0.6Sr0.4CoO3−δ forms a “super-reduced” solid solution before decomposing. When the sample underwent alternate reduction–oxidation, a hysteresis-like pO2 dependence of the oxygen content in the decomposition pO2 range was attributed to the reversible formation of ABO3 and A2BO4 phases. Reduction enthalpy and entropy were determined for the single-phase region and confirmed interpolated values from the literature.
Oxygen nonstoichiometry (shown as 3−δ) of La0.6Sr0.4CoO3−δ as a function of pO2 at 773–1173K. The experimental data were obtained by thermogravimetric analysis (TG) and coulometric titration (measured either by a simple reduction (CT1) or a “two-step-forward one-step-back” reduction–oxidation (CT2) procedure). D1 and D2 denote the decomposition pO2. The solid lines are the fit to the thermogravimetry and CT1 data. The dashed lines represent the non-equilibrium region where the sample shows a super-reduced state. Display omitted
► Oxygen nonstoichiometry of La0.6Sr0.4CoO3−δ at intermediate temperatures and p(O2). ► Experimental confirmation of previously interpolated reduction enthalpy. ► Decomposition p(O2) assessed by coulometric titration. ► Hysteresis-like p(O2) dependence of oxygen content at decomposition p(O2).
Summary Blood flow in active skeletal muscles provides energy substrate, oxygen and reduction of excessive heat and metabolic by‐products. Although cyclic jaw motions such as those during ...mastication and speech articulation are the primitive oro‐facial functions, possible effects of the cyclic muscle contractions on the intramuscular haemodynamics of the jaw muscles remains scarcely known. We investigated the masseteric haemodynamics during and after gum‐chewing. Ten healthy female adults participated in the study. Electromyography, kinetics of masseter muscle oxygenation, electrocardiogram and blood pressure were recorded simultaneously. The subjects were asked to perform gum‐chewing and cyclic jaw motion without gum bolus (empty‐chewing task). The haemodynamics parameters were compared between the two experimental conditions. During gum‐chewing task, deoxygenated haemoglobin and sympathetic nerve activity increased, while tissue blood oxygen saturation decreased. Blood pressure and parasympathetic nerve activity did not change. The overall behaviour of haemodynamic parameters during empty‐chewing task was similar to that observed during gum‐chewing task. However, the latency periods from the end of chewing until significant changes in the haemodynamic parameters were notably shorter (P < 0·05) in gum‐chewing task as compared with those associated with empty‐chewing task. The duration of the changes was shorter with empty‐chewing than with gum‐chewing. Fluctuations in masseter muscle haemodynamics associated with chewing jaw movement differed depending on the level of muscle contraction during movement. The differences became statistically significant immediately after the commencement of chewing and after the cessation movement. During the chewing movement, automatic nerve activities increased in response to the level of muscle contraction during movement.
We study the vibrational stability of model 2D solids with surfaces when large strains are present. For a fiber under compression, the phonon analysis correctly predicts the behavior of the buckling ...instability. For half-space under tension and compression, we find that (a) instabilities of the surface phonons, which are localized near the surface, almost always occur before bulk phonon instabilities; (b) with exceptions, short-wavelength or optical surface phonons usually go unstable first, rather than long-wavelength acoustic or elastic surface phonons; and (c) linear instability of a surface phonon triggers surface-initiated defect nucleation, such as dislocations or microcracks. The instability pattern seems to depend more on the surface structure than the interatomic potential model used.
To examine the effects of low-volume muscle endurance training on muscle oxidative capacity, endurance and strength of the forearm muscle during 21-day forearm immobilization (IMM-21d). The ...non-dominant arm (n = 15) was immobilized for 21 days with a cast and assigned to an immobilization-only group (Imm-group; n = 7) or an immobilization with training group (Imm+Tr-group; n = 8). Training comprised dynamic handgrip exercise at 30% of pre-intervention maximal voluntary contraction (MVC) at 1 Hz until exhaustion, twice a week during the immobilization period. The duration of each exercise session was 51.7 ± 3.4 s (mean ± SE). Muscle oxidative capacity was evaluated by the time constant for phosphocreatine recovery (τoffPCr) after a submaximal handgrip exercise using ³¹phosphorus-magnetic resonance spectroscopy. An endurance test was performed at 30% of pre-intervention MVC, at 1 Hz, until exhaustion. τoffPCr was significantly prolonged in the Imm-group after 21 days (42.0 ± 2.8 and 64.2 ± 5.1 s, pre- and post-intervention respectively; P < 0.01) but did not change for the Imm+Tr-group (50.3 ± 3.0 and 48.8 ± 5.0 s, ns). Endurance decreased significantly for the Imm-group (55.1 ± 5.1 and 44.7 ± 4.6 s, P < 0.05) but did not change for the Imm+Tr-group (47.9 ± 3.0 and 51.7 ± 4.0 s, ns). MVC decreased similarly in both groups (P < 0.01). Twice-weekly muscle endurance training sessions, each lasting approx. 50 s, effectively prevented a decrease in muscle oxidative capacity and endurance; however, there was no effect on MVC decline with IMM-21d.
Retinoid Signaling Determines Germ Cell Fate in Mice Bowles, Josephine; Knight, Deon; Smith, Christopher ...
Science (American Association for the Advancement of Science),
04/2006, Volume:
312, Issue:
5773
Journal Article
Peer reviewed
Germ cells in the mouse embryo can develop as oocytes or spermatogonia, depending on molecular cues that have not been identified. We found that retinoic acid, produced by mesonephroi of both sexes, ...causes germ cells in the ovary to enter meiosis and inititate oogenesis. Meiosis is retarded in the fetal testis by the action of the retinoid-degrading enzyme CYP26B1, ultimately leading to spermatogenesis. In testes of Cyp26b1-knockout mouse embryos, germ cells enter meiosis precociously, as if in a normal ovary. Thus, precise regulation of retinoid levels during fetal gonad development provides the molecular control mechanism that specifies germ cell fate.
La0.6Sr0.4Co1−yFeyO3−δ (LSCF) mixed-conducting perovskite oxides, a SOFC cathode candidate material, exhibit oxygen nonstoichiometry under reducing atmosphere and elevated temperatures. Reduction of ...the B-site transition metals and formation of oxygen vacancies result in chemical expansion of the LSCF lattice. Knowledge of both thermal and chemical lattice expansion as a function of composition is an essential tool to tailor mismatches between different materials exposed to reducing and high temperature environments and avoid mechanical failure of the device. In this paper, thermal and chemical expansion coefficients were determined by measurement of the lattice parameters by HT-XRD as a function of pO2 (in the range of 10−4 to 1bar), temperature (773–1173K) and B-site composition. The lattice parameters were correlated with the previously investigated oxygen nonstoichiometry of the LSCF series. While the thermal expansion coefficient increases almost linearly with increasing Co content, the chemical expansion coefficient appears to be independent of B-site composition.
•Lattice parameter of La0.6Sr0.4Co1−yFeyO3−δ as function of y, pO2 and T.•Trigonal and pseudocubic lattice parameters at RT follow Vegard's law.•Linear thermal expansion formulated based on “pure” thermal and chemical expansion.•Thermal expansion coefficient follows Vegard's law.•Chemical expansion coefficient independent of composition.
Summary The jerk‐cost is an index that can quantify the smoothness of various movements including human body movements. A previous study reported the usefulness of jerk‐cost in the evaluation of ...masticatory movement, and proposed that the masticatory movement of subjects with good occlusion could be explained as a maximum smooth movement. The purpose of this study was to investigate the influence of a single prosthetic molar restoration on the smoothness of masticatory movement. Fourteen adults who visited this hospital seeking a single prosthetic restoration on a molar were selected. Each subject chewed a piece of chewing gum on the molars of the treated side before and after crown placement. Movement trajectory was recorded using the Sirognathograph Analyzing System. Normalized jerk‐cost (NJC) was calculated on the closing phase of each chewing cycle and was compared before and after the crown placement. After the prosthetic restoration, NJC significantly decreased (P < 0·05) in seven subjects with a crown placed on a lower molar, whereas significant changes were not observed in seven subjects with a crown placed on an upper molar. These results suggest that restoring a crown on a lower molar could significantly improve the smoothness of masticatory movement on the same side.
