43 research outputs found
Structurally Dependent Fano Resonances in the Infrared Spectra of Phonons in Few-Layer Graphene
The in-plane optical phonons around 200 meV in few-layer graphene are
investigated utilizing infrared absorption spectroscopy. The phonon spectra
exhibit unusual asymmetric features characteristic of Fano resonances, which
depend critically on the layer thickness and stacking order of the sample. The
phonon intensities in samples with rhombohedral (ABC) stacking are
significantly higher than those with Bernal (AB) stacking. These observations
reflect the strong coupling between phonons and interband electronic
transitions in these systems and the distinctive variation in the joint density
of electronic states in samples of differing thickness and stacking order.Comment: 20 pages, 7 figures, supplementary material include
Measurement of the Optical Conductivity of Graphene
Optical reflectivity and transmission measurements over photon energies
between 0.2 and 1.2 eV were performed on single-crystal graphene samples on a
transparent SiO2 substrate. For photon energies above 0.5 eV, graphene yielded
a spectrally flat optical absorbance of (2.3 +/- 0.2)%. This result is in
agreement with a constant absorbance of pi*alpha, or a sheet conductivity of
pi*e^2/2h, predicted within a model of non-interacting massless Dirac Fermions.
This simple result breaks down at lower photon energies, where both spectral
and sample-to-sample variations were observed. This "non-universal" behavior is
explained by including the effects of doping and finite temperature, as well as
contributions from intraband transitions.Comment: 9 pages, 4 figures, Phys. Rev. Lett. 101, 196405 (2008
A non-invasive biomechanical device to quantify knee rotational laxity: Verification of the device in human cadaveric specimens
Background: Biomechanical measurement tools have been developed and widely used to precisely
quantify knee anterior-posterior laxity after anterior cruciate ligament (ACL) injury. However, validated
objective device to document knee rotational laxity, though being developed by different researchers, are
not yet widely used in the daily clinical practice. A new biomechanical device was developed to quantify
knee internal and external rotations.
Methods: The reliability of the new biomechanical device which measures knee rotations were tested.
Different torques (1-10Nm) were applied by the device to internally and externally rotate human
cadaveric knees, which were held in a flexion angle of 30 . The rotations were measured by the device in
degrees. There were two independent testers, and each tester carried out three trials. Intra-rater and
inter-rater reliability were quantified in terms of intraclass correlation (ICC) coefficient among trials and
between testers. The device was verified by the comparison with a computer assisted navigation system.
ICC was measured. Mean, standard deviation and 95% confident interval of the difference as well as the
root mean square difference were calculated. The correlations were deemed to be reliable if the ICC was
above 0.75.
Results: The intra-rater and inter-rater reliability achieved high correlation for both internal and external
rotation, ranged from 0.959 to 0.992. ICC between the proposed meter and the navigation system for
both internal and external rotation was 0.78. The mean differences were 2.3 and 2.5 for internal and
external rotation respectively.
Conclusions: A new knee rotational laxity meter was proposed in this study. Its reliability was verified by
showing high correlation among trials. It also showed good correlation to a gold standard of measurement. It might be used to document knee rotational laxity for various purposes, especially after ACL
injury, after further validation of the device in human subject
Is 'oil pulling' a 'snake oil'? : a clinical trial
The traditional Ayurveda practice of ‘oil pulling’ has become a recent phenomenon and concerns about its efficacy have been raised. Objectives: (1) to determine awareness about the practice of ‘oil pulling’ among a group of young adults, and to determine variations in awareness with respect to socio-demographic factors, oral health behaviours (oral hygiene and dental attendance) and use of natural health products; (2) to determine the effectiveness of ‘oil pulling’ and conventional oral hygiene practice compared to the use of conventional oral hygiene practice alone in terms of oral hygiene and (3) to determine the effectiveness of ‘oil pulling’ and conventional oral hygiene practice compared to the use of conventional oral hygiene practice alone in terms of gingival health. Methods: Group members recruited seventy-four young adults to participate in a clinical trial over a two-month period comparing the effectiveness of (a) ‘oil pulling’ and conventional oral hygiene methods (toothbrush and toothpaste) versus (b) conventional oral hygiene methods alone. Oral hygiene was assessed using the Plaque Index - PI (Silness and Löe, 1964) and the proportion of sites with visible plaque (PVP). Gingival health was assessed using the Gingival Index – GI (Silness and Löe,1963) and the proportion of sites with gingival bleeding (PGB). Participants were block randomized in groups of four to a cross over clinical trial and assessments were conducted at one-month and two-months. Results: Approximately a quarter (28.4%, 21) of participants was aware of the practice of ‘oil pulling’. Awareness of the practice was associated with reported use of natural dental/oral health products (p0.05). There were observed significant differences in gingival health among both the test and control groups from baseline to one-month (p0.05). No significant differences were observed in oral health parameters from one-month to two-month among neither the test nor control groups (p>0.05). Conclusion: Awareness of the practice of ‘oil pulling’ is relatively common and is associated with use of natural dental/oral health products. Findings from the clinical trial failed to support the adjunct use of ‘oil pulling’ in addition to conventional oral hygiene practices.published_or_final_versio
Observation of an electrically tunable band gap in trilayer graphene
A striking feature of bilayer graphene is the induction of a significant band
gap in the electronic states by the application of a perpendicular electric
field. Thicker graphene layers are also highly attractive materials. The
ability to produce a band gap in these systems is of great fundamental and
practical interest. Both experimental and theoretical investigations of
graphene trilayers with the typical ABA layer stacking have, however, revealed
the lack of any appreciable induced gap. Here we contrast this behavior with
that exhibited by graphene trilayers with ABC crystallographic stacking. The
symmetry of this structure is similar to that of AB stacked graphene bilayers
and, as shown by infrared conductivity measurements, permits a large band gap
to be formed by an applied electric field. Our results demonstrate the critical
and hitherto neglected role of the crystallographic stacking sequence on the
induction of a band gap in few-layer graphene.Comment: 10 pages, 5 figures, including the supplementary information on the
electron-hole asymmetry of ABA-stacked trilaye
Induced Pluripotent Stem Cells-Derived Mesenchymal Stem Cells Attenuate Cigarette Smoke-Induced Cardiac Remodeling and Dysfunction
The strong relationship between cigarette smoking and cardiovascular disease (CVD) has been well-documented, but the mechanisms by which smoking increases CVD risk appear to be multifactorial and incompletely understood. Mesenchymal stem cells (MSCs) are regarded as an important candidate for cell-based therapy in CVD. We hypothesized that MSCs derived from induced pluripotent stem cell (iPSC-MSCs) or bone marrow (BM-MSCs) might alleviate cigarette smoke (CS)-induced cardiac injury. This study aimed to investigate the effects of BM-MSCs or iPSC-MSCs on CS-induced changes in serum and cardiac lipid profiles, oxidative stress and inflammation as well as cardiac function in a rat model of passive smoking. Male Sprague-Dawley rats were randomly selected for exposure to either sham air (SA) as control or 4% CS for 1 h per day for 56 days. On day 29 and 43, human adult BM-MSCs, iPSC-MSCs or PBS were administered intravenously to CS-exposed rats. Results from echocardiography, serum and cardiac lipid profiles, cardiac antioxidant capacity, cardiac pro- and anti-inflammatory cytokines and cardiac morphological changes were evaluated at the end of treatment. iPSC-MSC-treated group showed a greater effect in the improvement of CS-induced cardiac dysfunction over BM-MSCs-treated group as shown by increased percentage left ventricular ejection fraction and percentage fractional shortening, in line with the greater reversal of cardiac lipid abnormality. In addition, iPSC-MSCs administration attenuated CS-induced elevation of cardiac pro-inflammatory cytokines as well as restoration of anti-inflammatory cytokines and anti-oxidative markers, leading to ameliorate cardiac morphological abnormalities. These data suggest that iPSC-MSCs on one hand may restore CS-induced cardiac lipid abnormality and on the other hand may attenuate cardiac oxidative stress and inflammation via inhibition of CS-induced NF-κB activation, leading to improvement of cardiac remodeling and dysfunction. Thus, iPSC-MSCs may be a promising candidate in cell-based therapy to prevent cardiac complications in smokers
Observation of out-of-plane vibrations in few-layer graphene
We report the observation of layer breathing mode (LBM) vibrations in
few-layer graphene (FLG) samples of thickness from 2 to 6 layers, exhibiting
both Bernal (AB) and rhombohedral (ABC) stacking order. The LBM vibrations are
identified using a Raman combination band lying around 1720 cm-1. From double
resonance theory, we identify the feature as the LOZO' combination mode of the
out-of-plane LBM (ZO') and the in-plane longitudinal optical mode (LO). The
LOZO' Raman band is found to exhibit multiple peaks, with a unique line shape
for each layer thickness and stacking order. These complex line shapes of the
LOZO'-mode arise both from the material-dependent selection of different
phonons in the double-resonance Raman process and from the detailed structure
of the different branches of LBM in FLG.Comment: 17 pages, 7 figures, supplemental material include