Photoinduced Energy Transfer in Linear Guest-Host Chromophores: A Computational Study.

Polymer-based guest-host systems represent a promising class of materials for efficient light-emitting diodes. The energy transfer from the polymer host to the guest is the key process in light generation. Therefore, microscopic descriptions of the different mechanisms involved in the energy transfer can contribute to enlighten the basis of the highly efficient light harvesting observed in this kind of materials. Herein, the nature of intramolecular energy transfer in a dye-end-capped conjugated polymer is explored by using atomistic nonadiabatic excited-state molecular dynamics. Linear perylene end-capped (PEC) polyindenofluorenes (PIF), consisting of n (n = 2, 4, and 6) repeat units, i.e., PEC-PIFn oligomers, are considered as model systems. After photoexcitation at the oligomer absorption maximum, an initial exciton becomes self-trapped on one of the monomer units (donors). Thereafter, an efficient ultrafast through-space energy transfer from this unit to the perylene acceptor takes place. We observe that this energy transfer occurs equally well from any monomer unit on the chain. Effective specific vibronic couplings between each monomer and the acceptor are identified. These oligomer → end-cap energy transfer steps do not match with the rates predicted by Förster-type energy transfer. The through-space and through-bond mechanisms are two distinct channels of energy transfer. The former dominates the overall process, whereas the through-bond energy transfer between indenofluorene monomer units along the oligomer backbone only makes a minor contribution.

Vibrational energy redistribution during donor-acceptor electronic energy transfer: criteria to identify subsets of active normal modes.

Photoinduced electronic energy transfer in conjugated donor-acceptor systems is naturally accompanied by intramolecular vibrational energy redistributions accepting an excess of electronic energy. Herein, we simulate these processes in a covalently linked donor-acceptor molecular dyad system by using nonadiabatic excited state molecular dynamics simulations. We analyze different complementary criteria to systematically identify the subset of vibrational normal modes that actively participate on the donor → acceptor (S2→ S1) electronic relaxation. We analyze energy transfer coordinates in terms of state-specific normal modes defined according to the different potential energy surfaces (PESs) involved. On one hand, we identify those vibrations that contribute the most to the direction of the main driving force on the nuclei during electronic transitions, represented by the non-adiabatic derivative coupling vector between donor and acceptor electronic states. On the other hand, we monitor normal mode transient accumulations of excess energy and their intramolecular energy redistribution fluxes. We observe that the subset of active modes varies according to the PES on which they belong and these modes experience the most significant rearrangements and mixing. Whereas the nuclear motions that promote donor → acceptor energy funneling can be localized mainly on one or two normal modes of the S2 state, they become spread out across multiple normal modes of the S1 state following the energy transfer event.

The effect of foot overpronation on Achilles tendon blood supply in healthy male subjects.

The purpose of this study was to investigate Achilles tendon blood flow in individuals with overpronated feet during non-weight- and weight-bearing positions. Achilles tendon blood flow was measured by means of the pulsatility index (PI) and the resistance index (RI) in 15 male individuals with overpronated feet and 15 counterparts with normal feet, using power Doppler ultrasonography (PDI). Achilles tendon ultrasonographic (US) assessment was performed at its musculo-tendinous junction (MTJ), mid-tendon (MT), and osseotendinous junction (OTJ) at a non-weight-bearing relaxed position (RP) and during two-leg stance (TLS) and one-leg upright stance (OLS). PI and RI indices were significantly greater in individuals with overpronated feet compared to individuals with normal feet at the OTJ in OLS position (P < 0.01), and at MT in both TLS (P < 0.001) and OLS positions (P < 0.001). All individuals demonstrated also greater PI and RI indices at MT followed by the OTJ and MTJ in all positions (P < 0.001), and in OLS compared to TLS and the RP at the OTJ (P < 0.01) as well as at MT and MTJ (P < 0.001). The findings of the present study suggest that foot overpronation may affect Achilles tendon blood flow, particularly at mid-tendon, thus enhancing the possibility for injury.

Heritability of the rate of torque development.

AIM: The aim of this study was to estimate the genetic and environmental contribution to the variation observed in the rate of torque development (RTD), which is considered an important determinant of sport performance. METHODS: Nine monozygotic (MZ) and seven dizygotic (DZ) twin pairs, of both sexes aged 19-26 years, performed three isometric maximal voluntary contractions with the knee at 70 degrees and 40 degrees of flexion (0 degrees=terminal extension) on a Contrex Isokinetic dynamometer. The RTD was extracted from the force time curves and calculated in two different ways, giving rise to two indices, the maximal rate of torque development (MRTD), and the torque at the first 100 msec (F100msec). Heritability estimates (h2) were derived on the basis of intrapair variances between MZ and DZ twin pairs. RESULTS: A significant genetic influence (P<0.05) was found for both RTD indices (h2=0.99, and 0.93 for MRTD, and F100msec respectively) at only 40 degrees of knee flexion, an angle associated with intensive neural activation. CONCLUSION: The maximal rate of torque development of knee extensor muscles during the initial phase of their contraction and at enhanced neural activation, is under strong genetic influence.

Cross-cultural adaptation of the Greek version of the Knee Outcome Survey--activities of Daily Living Scale (KOS-ADLS).

The purpose of this study was to cross-culturally adapt and validate the Greek version of Knee Outcome Survey-Activities of Daily Living Scale (KOS-ADLS), a self-reported instrument used for patients with various knee pathological conditions including osteoarthritis. Ninety-four patients (57 males and 37 females) with a variety of pathological knee disorders and impairments being referred to physical therapy for evaluation and treatment were included in the study. For the crοss-cultural translation, a back-translation procedure was utilized by 3 bi-lingual translators. To assess test-retest reliability the patients were asked to complete the KOS-ADLS twice at initial visit; before and after physiotherapy treatment. To assess responsiveness, patients completed the KOS-ADLS at the end of all physiotherapy sessions and the score was compared with KOS-ADLS at initial (pre-treatment) visit. Finally, concurrent validity was measured by comparing the responses to the KOS-ADLS scores against the scores obtained from Visual Analogue Scale (VAS) and Global Rating Scale (GRS). Reliability was found satisfactory (ICC=0.97; SEM=3.03; SDD=23.05; Cronbach's alpha=0.98). Moreover, a gender subgroup analysis showed that women were more reliable than men. Minor floor/ceiling effects were detected. Concerning validity, all correlations were statistically significant, ranging from r=0.315 to r=0.741, however GRS presented higher correlations with KOS-ADLS in comparison with VAS. Finally, Greek KOS-ADLS was able to detect changes over time (standardized effect size=1.31 and standardized response mean=1.64). The Greek version of KOS-ADLS was found to be reliable, valid, responsive and comprehensible to use with patients with knee pathology.

2D excitons as primary energy carriers in organic crystals: the case of oligoacenes.

A number of organic crystals show anisotropic excitonic couplings, with weak interlayer interactions between molecules that are more strongly coupled within the layers. The resulting energy carriers are intralayer 2D excitons that diffuse along the interlayer direction. We model this analytically for infinite layers and using quantum-chemical calculations of the electronic couplings for anthracene clusters. We show that the exciton hopping rates and diffusion lengths depend in a subtle manner on the size and shape of the interacting aggregates, temperature, and the presence of energetic disorder.

Eversion and inversion muscle group peak torque in hyperpronated and normal individuals.

BACKGROUND: Excessive subtalar pronation causes significant changes in the biomechanics of the lower leg, adversely influences proprioceptive feedback and neuromuscular reflex behavior and consequently, affects stability of the foot. However, the changes in muscle strength, caused by hyperpronation are unclear. OBJECTIVES: The purpose of the present study was to compare the evertor and invertor peak torque between hyperpronated and normal individuals as well as between their dominant and non-dominant foot. METHOD: 20 healthy male participants volunteered for this study. Leg dominance was assessed on the basis of a questionnaire and navicular drop measurements were used to classify participants into two groups: hyperpronated (> or =10 mm) and normals (5-9 mm). Isokinetic concentric eversion and inversion muscle group strength was tested at 30 degrees and 120 degrees/s using the Con-Trex MJ isokinetic dynamometer. RESULTS: In all cases, inversion peak torque was greater than eversion peak torque and declined with increasing angular velocity. No significant differences were found for inversion and eversion concentric strength at both speeds tested, neither between normal and hyperpronated individuals neither between their dominant and non-dominant foot. CONCLUSIONS: These results indicate the need re-evaluation of navicular drop values in order to identify normal and abnormal subtalar pronation. The assessment of eccentric contractions is also proposed when examining invertors and evertors isokinetic strength.

Development, reliability and validity of a new motorized isometric dynamometer for measuring strength characteristics of elbow flexor muscles.

The aim of this study was to develop a new apparatus capable of accurately recording and analysing torque-time curve during isometric muscle contractions of the elbow flexors. A total of 25 (age 29.3+/-5.0 years) non-athlete male volunteers participated in this study. To establish the measurement precision of the new testing apparatus and to determine possible sources of error in the results, a series of tests was performed. Instrument validity was assessed by comparing each selected measure (lever arm angular position, torque and maximal isometric torque) to a criterion (external inclinometer, calibrated weights and isokinetic dynamometer, respectively), while trial-to-trial and day-to-day comparisons of measurements were made to estimate the reproducibility of the instrument. The statistical outcomes of validity tests demonstrated high agreement between measures and associated criteria (Pearson correlation coefficient's values >.97). Trial-to-trial correlations for maximal isometric torque in different elbow angles showed excellent reproducibility, as values of intraclass correlation coefficient (ICC([2,1])) ranged from 0.889 to 0.971, with higher value in the middle angle (90 degrees ). The value of ICC([2,1]) (day-to-day) for maximal isometric torque in 90 degrees was 0.986 and the respective standard error of measurement (SEM) was 1.5 Nm. Our results indicate that the isometric evaluation of elbow flexor muscles with the new dynamometer is accurate and reproducible.

The effect of different skin-ankle brace application pressures with and without shoes on single-limb balance, electromyographic activation onset and peroneal reaction time of lower limb muscles.

BACKGROUND: Several studies have been carried out in order to investigate the effect of ankle bracing on ankle joint function and performance. However, no study so far has examined the role of skin-brace interface pressure in neuromuscular control. The aim of this study was to investigate the effect of different skin-ankle brace interface pressures, with and without shoes, on quiet single-limb balance and the electromyographic (EMG) activation sequence of four lower limb muscles. METHODS: Twelve male physical education students who volunteered to take part in the study were measured with and without shoes under three ankle brace conditions: (i) without brace, (ii) with brace and 30 kilopascals (kPa) application pressure and (iii) with brace and 60 kPa application pressure. Single-limb balance (anteroposterior and mediolateral parameter) was assessed on the dominant lower limb, with open and closed eyes, on a force platform, simultaneously with the EMG recording of four lower lower limb muscles' (gastrocnemius, peroneus longus, rectus femoris and biceps femoris) activation onset. Peroneus longus reaction time was also measured by provoking a sudden subtalar inversion stress test using a trap-door. RESULTS: The results showed that the application of athletic footwear resulted in a significant difference between the condition with shoes and without shoes, with a significantly increased anteroposterior sway and sway velocity, in all three ankle brace application conditions with shoes (F=50.9, d.f.=1, p<0.001 and F=58.4, d.f.=1, p<0.001), but had no effect in the mediolateral stability, or the total stability parameter. Shoes had no significant effect on the EMG activation sequence of the four lower limb muscles. Lastly, ankle brace application with 30 and 60 kPa application pressures, with and without athletic footwear, led to a significant delay in the peroneus longus reaction time (F=9.71, d.f.=2, p<0.001). CONCLUSIONS: These findings suggest that different ankle brace application pressures may have an effect on single-limb balance, and peroneal reaction time. The application of athletic footwear, further adversely affects these parameters significantly. Further research is needed in this area with more dynamic and functional measurements, before the safe use of ankle bracing can be widely recommended.

Effects of baseline serum levels of Se on markers of eccentric exercise-induced muscle injury.

Inflammation and oxidative stress have been implicated in the mechanism of eccentric exercise-induced muscle injury. This study examined whether baseline serum levels of selenium (Se), a trace element that participates in both antioxidant and anti-inflammatory systems, affects the overall response to injury. Thirteen males performed 36 maximal eccentric actions with the elbow flexors of the non-dominant arm on a motorized dynamometer. Venous blood samples were collected immediately before and after exercise at 2, 24, 48, 72 and 96 hours. Established indicators of muscle damage such as maximum isometric torque (MIT), range of motion (ROM), relaxed arm angle (RANG), flexed arm angle (FANG), arm circumference (CIRC), muscle soreness and serum levels of creatine kinase (CK) and lactate dehydrogenase (LDH) were determined at the same time points. Baseline serum levels of Se were also measured. Complementary data regarding assessment of Se status were retrieved by the use of a semi-quantitative food frequency questionnaire. All measures changed significantly (p<0.05) after exercise. The main finding of this study was that baseline Se serum levels were associated inversely with CK, LDH and FANG and positively with MIT and ROM (p<0.05). These data suggest that beyond overt Se deficiency, suboptimal Se status possibly worsens muscle functional decrements subsequent to eccentric muscle contractions.

The effects of strength training, cardiovascular training and their combination on flexibility of inactive older adults.

The purpose of this study was to investigate the effects of aerobic training, strength training and their combination on joint range of motion of inactive older individuals. Thirty-two inactive older men (65 - 78 yr) were assigned to one of four groups (n = 8 per group): control (C), strength training (ST), cardiovascular training (CT), and combination of strength and aerobic training (SA). Subjects in the S, A, and SA trained three times a week for 16 weeks. ST included 10 resistance exercises for the major muscle groups at an intensity of 55 - 80% of 1-RM and CT included walking/jogging at 50 - 80 % of maximal heart rate. Body weight and height, physical activity level and maximal oxygen uptake (.VO(2)max) were measured before the training period. Isokinetic (60 and 180 deg x sec(-1)) and concentric strength (1-RM in bench and leg press) were assessed prior to and at the end of the training period. Hip flexion, extension, abduction, and adduction, shoulder extension, flexion, and adduction, knee flexion, elbow flexion and sit-and-reach score were determined before and at 8 and 16 weeks of training. There were no differences between groups in .VO(2)max, body weight, and height (p < 0.05). ST and SA but not CT and C increased isokinetic and concentric strength at the end of the training period (p < 0.05). ST and SA increased significantly (p < 0.05) sit-and-reach performance, elbow flexion, knee flexion, shoulder flexion and extension and hip flexion and extension both at mid- and post-training. CT increased (p < 0.05) only hip flexion and extension at post training. Results indicate that resistance training may be able to increase range of motion of a number of joints of inactive older individuals possibly due to an improvement in muscle strength.

The effect of aerobic training in girls with idiopathic scoliosis.

The purpose of the present study was to investigate the effect of aerobic training in girls with idiopathic scoliosis, in selective respiratory parameters (VC, FVC, FEV1, FEV1/VC% FEV1/FVC) as well as the ability to perform aerobic work (PWC170). The training group consisted of 20 young girls with a mean age of 13.5 +/- 0.16 years. They wore a Boston-type brace for a mean period of 0.30 +/- 0.04 years and suffered from a scoliotic curve (27.4 +/- 1.9 degrees). They followed a two-month training program on the cycloergometer. Each training session lasted 30 min and was performed four times a week. The control group consisted of 20 girls with a mean age of 13.6 +/- 0.18 years and they wore the same type of brace for a mean period of 0.24 +/- 0.04 years. They also suffered from a scoliosis (29.5 +/- 1.8 degrees). The results of the study revealed that aerobic training sustained (VC, FEV1, FEV1/VC) or improved significantly (FVC, FEV1/FVC) the parameters of pulmonary function, while the respective parameters (VC, FVC) for the control group were reduced during the two-month period. The ability to perform aerobic work increased 48.1% (P < 0.01) in the training group, while it decreased 9.2% (P < 0.01) in the control group.