Systematic determination of absolute absorption cross-section of individual carbon nanotubes

Optical absorption is the most fundamental optical property characterizing light–matter interactions in materials and can be most readily compared with theoretical predictions. However, determination of optical absorption cross-section of individual nanostructures is experimentally challenging due to the small extinction signal using conventional transmission measurements. Recently, dramatic increase of optical contrast from individual carbon nanotubes has been successfully achieved with a polarization-based homodyne microscope, where the scattered light wave from the nanostructure interferes with the optimized reference signal (the reflected/transmitted light). Here we demonstrate high-sensitivity absorption spectroscopy for individual single-walled carbon nanotubes by combining the polarization-based homodyne technique with broadband supercontinuum excitation in transmission configuration. To our knowledge, this is the first time that high-throughput and quantitative determination of nanotube absorption cross-section over broad spectral range at the single-tube level was performed for more than 50 individual chirality-defined single-walled nanotubes. Our data reveal chirality-dependent behaviors of exciton resonances in carbon nanotubes, where the exciton oscillator strength exhibits a universal scaling law with the nanotube diameter and the transition order. The exciton linewidth (characterizing the exciton lifetime) varies strongly in different nanotubes, and on average it increases linearly with the transition energy. In addition, we establish an empirical formula by extrapolating our data to predict the absorption cross-section spectrum for any given nanotube. The quantitative information of absorption cross-section in a broad spectral range and all nanotube species not only provides new insight into the unique photophysics in one-dimensional carbon nanotubes, but also enables absolute determination of optical quantum efficiencies in important photoluminescence and photovoltaic processes.Single-walled carbon nanotubes (SWNTs), a model one-dimensional nanomaterial system, constitute a rich family of structures (1). Each single-walled nanotube structure, uniquely defined by the chiral index (n,m), exhibits distinct electrical and optical properties (2–5). Quantitative information of SWNT absorption cross-section is highly desirable for understanding nanotube electronic structures, for evaluating quantum efficiency of nanotube photoluminescence (5, 6) and photocurrent (7–9), and for investigating the unique many-body effects in 1D systems (10–16). Despite its obvious importance, reliable experimental determination of nanotube absorption cross-section at the single-tube level is still challenging (17). Previous absorption measurements on ensemble nanotube samples only provide averaged behavior (18–20). Recent absorption studies of individual nanotubes, suffering from small absorption signals and/or slow laser-frequency scanning, cannot determine the absolute absorption cross-section and are limited in achievable spectral range (15, 21–23).We demonstrate here a high-sensitivity polarization-based homodyne method to measure nanotube absorption spectra. By manipulating the light polarization, we enhanced the nanotube-induced transmission contrast, ΔI/I, by two orders of magnitude, and this enhanced transmission contrast can be quantitatively related to nanotube absorption cross-section along and perpendicular to the nanotube axis. Using this polarization control together with supercontinuum laser source, we realized high-throughput and broadband absorption measurements at the single-tube level; combined with electron diffraction technique on the same tube, it enables absolute determination of absorption cross-sections of individual chirality-defined nanotubes, to our knowledge for the first time. We obtained quantitative absorption spectra of over 50 SWNTs of different chiralities, and established a phenomenological formula for absorption cross-sections of different nanotubes. The chirality-dependent nanotube absorption spectra reveal unique 1D photophysics in nanotubes, including a universal scaling behavior of exciton oscillator strength and of exciton resonance linewidth.     

Computerized ultrasonic axiographic evaluation of condylar movement in patients with internal derangement of the temporomandibular joint

Objectives:To evaluate condylar movement during lateral excursion in individuals with internal derangement of the temporomandibular joint (TMJ) using ultrasonic axiography.Materials and Methods:A total of 34 patients with internal derangement of the TMJ and 34 participants in the control group were examined. Mandibular functional movement was recorded by ultrasonic axiography. Three-dimensional condylar movement was measured in the working and balancing condyles.Results:Significant differences in condylar movement were found between the two groups. In the group with internal derangement of the TMJ, the three-dimensional linear distances of the condylar path in a working condyle were greater than in the control group during lateral excursion. The speed of the balancing condyle in the returning path of lateral excursion was significantly greater in the group with internal derangement than in the control group.Conclusions:The results of the present study indicate that internal derangement of TMJ may affect the working and balancing condylar movements during lateral excursion.     

Derivation of na?ve human embryonic stem cells

The naïve pluripotent state has been shown in mice to lead to broad and more robust developmental potential relative to primed mouse epiblast cells. The human naïve ES cell state has eluded derivation without the use of transgenes, and forced expression of OCT4, KLF4, and KLF2 allows maintenance of human cells in a naïve state [Hanna J, et al. (2010) Proc Natl Acad Sci USA 107(20):9222–9227]. We describe two routes to generate nontransgenic naïve human ES cells (hESCs). The first is by reverse toggling of preexisting primed hESC lines by preculture in the histone deacetylase inhibitors butyrate and suberoylanilide hydroxamic acid, followed by culture in MEK/ERK and GSK3 inhibitors (2i) with FGF2. The second route is by direct derivation from a human embryo in 2i with FGF2. We show that human naïve cells meet mouse criteria for the naïve state by growth characteristics, antibody labeling profile, gene expression, X-inactivation profile, mitochondrial morphology, microRNA profile and development in the context of teratomas. hESCs can exist in a naïve state without the need for transgenes. Direct derivation is an elusive, but attainable, process, leading to cells at the earliest stage of in vitro pluripotency described for humans. Reverse toggling of primed cells to naïve is efficient and reproducible.It has become clear with the derivation of mouse epiblast stem cells (mEpiSCs) that pluripotency encompasses more than one stage of development (1, 2). The earlier “naïve” stage represents the preimplantation inner cell mass, typified by mouse ES cells (mESCs), and the “primed,” the postimplantation epiblast, typified by mEpiSCs and human ES cells (hESCs). The challenge in naïve cell maintenance has been protecting cells from differentiation stimuli. This has been achieved in mESCs through exposure to leukemia inhibitory factor (LIF), whereas addition of extracellular signal-regulated kinase (MEK) and glycogen synthase kinase 3 (GSK3) inhibitors (2i) in defined medium allows the cells to attain a homogeneous ground state (3). Defining characteristics of the naïve/ground vs. primed states are shown in Fig. S1A. In humans, the naïve stage has been difficult to capture as a stable in vitro state.There are practical advantages that come with a human naïve state. Among them is ease of trypsin passage and developmental capacity. Whole animals can be generated from good naïve mESCs through tetraploid complementation (4), and mEpiSCs cannot contribute to chimerism. Being more comparable to mESCs, naïve hESCs will likely allow increased developmental potential and a more accurate correlation to mESC data.It has been reported that human induced pluripotent cells (h-iPSCs) can be maintained in the naïve state if the pluripotency-inducing transgenes are not silenced (5). Only recently have hESCs been maintained in a naïve state without transgenes (6). Our primary aim was to generate naïve hESCs not dependent upon transgenes for stable culture. We toggled existing human ESC and mouse mEpiSC lines back from the primed state to grow under the influence of 2i without the need for Activin A. This helped us to define appropriate culture conditions for human naïve cells and allowed the de novo derivation of a naïve hESC line, Elf1. We report on the naïve state of human ESCs capable of unlimited culture in 2i.     

High prevalence of low bone mass and associated factors in Korean HIV-positive male patients undergoing antiretroviral therapy

Introduction

Low bone mass is prevalent in HIV-positive patients. However, compared to Western countries, less is known about HIV-associated osteopenia in Asian populations.

Methods

We performed a cross-sectional survey in Seoul National University Hospital from December 2011 to May 2012. We measured bone mineral density using central dual energy X-ray absorptiometry, with consent, in male HIV-positive patients, aged 40 years and older. Diagnosis of low bone mass was made using International Society for Clinical Densitometry Z-score criteria in the 40–49 years age group and World Health Organization T-score criteria in the >50-year age group. The data were compared with those of a community-based cohort in Korea.

Results

Eighty-four HIV-positive male patients were included in this study. Median age was 49 (interquartile range [IQR], 45–56) years, and median body mass index (BMI) was 22.6 (IQR, 20.9–24.4). Viral suppression was achieved in 75 (89.3%) patients and median duration of antiretroviral therapy was 71 (IQR, 36–120) months. The overall prevalence of low bone mass was 16.7% in the 40–49 years age group and 54.8% in the>50 years age group. Our cohort had significantly lower bone mass at the femur neck and total hip than HIV-negative Koreans in the 40–49 years age group. Low bone mass was significantly associated with low BMI, and a high level of serum carboxy-terminal collagen crosslinks, but was not associated with antiretroviral regimen or duration of antiretroviral therapy.

Conclusions

Low bone mass is prevalent in Korean HIV-positive males undergoing antiretroviral therapy, and may be associated with increased bone resorption.     

Does Well Maintained Graft Provide Consistent Return to Play after Medial Ulnar Collateral Ligament Reconstruction of the Elbow Joint in Elite Baseball Players?

Background

Several studies have reported the clinical outcomes of medial ulnar collateral ligament (MUCL) reconstruction of the elbow joint in throwing athletes, including the rate of return to sports. However, little has been known about the imaging outcomes after MUCL reconstruction. The aim of this study is to report the clinical and imaging outcomes after MUCL reconstruction using figure of eight fashion in the elite and professional baseball players.

Methods

This study included 17 baseball players, who underwent MUCL reconstruction between July 2007 and May 2010. The average follow-up period was 48.6 months. Imaging assessment consisted of preoperative plain and stress radiographs, magnetic resonance imaging, and postoperative serial ultrasonography. The clinical assessments were composed of visual analogue scale (VAS) for pain, range of motion, and the Conway scale.

Results

The mean VAS score was 6.4 (range, 3 to 8) preoperatively and 2.2 (range, 0 to 4) postoperatively (p < 0.05). There were nine players (53%) classified as excellent who returned to sports at the same or higher level compared to preinjury. Serial ultrasonography revealed well-maintained grafts at 3 and 12 months in all of the players. Five out of 17 players showed decreased echogenecity in the common flexor tendon at 3 months, which was considered as remaining tissue swelling and resolved completely at 12 months.

Conclusions

All grafts are well-maintained until 12-months based on the ultrasonographic findings, although only 53% of the players returned to preinjury level.     

Tumor Treated by Endoscopy

Background

This study was conducted to examine the clinical usefulness and efficacy of endoscopic curettage on benign bone tumor.

Methods

Thirty-two patients (20 men and 12 women) with benign bone tumor were included in the study. The patients were aged between five and 76 years; the mean follow-up period was 27.05 months (range, 9.6 to 39.9 months). The primary sites include simple bone cyst (9 cases), fibrous dysplasia (6 cases), enchondroma (5 cases), non-ossifying fibroma (4 cases), bone infarct (3 cases), aneurysmal bone cyst (1 case), chondroblastoma (1 case), osteoblastoma (1 case), intraosseous lipoma (1 case), and Brodie abscess (1 case). A plain radiography was performed to assess the radiological recovery. Radiological outcomes, including local recurrence and bone union, were evaluated as excellent, good, poor, and recurred.

Results

In our series, there were 27 cases (84.4%) of good or better outcomes, six cases (18.8%) of complications (4 local recurrence, 1 wound infection, and 1 pathologic fracture).

Conclusions

Our results showed that endoscopic curettage and bone graft had a lower rate of recurrence and a higher cure rate in cases of benign bone tumor. It can, therefore, be concluded that endoscopic curettage and bone graft might be good treatment modalities for benign bone tumors.