Atomic clock performance enabling geodesy below the centimetre level.

The passage of time is tracked by counting oscillations of a frequency reference, such as Earth's revolutions or swings of a pendulum. By referencing atomic transitions, frequency (and thus time) can be measured more precisely than any other physical quantity, with the current generation of optical atomic clocks reporting fractional performance below the 10-17 level1-5. However, the theory of relativity prescribes that the passage of time is not absolute, but is affected by an observer's reference frame. Consequently, clock measurements exhibit sensitivity to relative velocity, acceleration and gravity potential. Here we demonstrate local optical clock measurements that surpass the current ability to account for the gravitational distortion of space-time across the surface of Earth. In two independent ytterbium optical lattice clocks, we demonstrate unprecedented values of three fundamental benchmarks of clock performance. In units of the clock frequency, we report systematic uncertainty of 1.4 × 10-18, measurement instability of 3.2 × 10-19 and reproducibility characterized by ten blinded frequency comparisons, yielding a frequency difference of [-7 ± (5)stat ± (8)sys] × 10-19, where 'stat' and 'sys' indicate statistical and systematic uncertainty, respectively. Although sensitivity to differences in gravity potential could degrade the performance of the clocks as terrestrial standards of time, this same sensitivity can be used as a very sensitive probe of geopotential5-9. Near the surface of Earth, clock comparisons at the 1 × 10-18 level provide a resolution of one centimetre along the direction of gravity, so the performance of these clocks should enable geodesy beyond the state-of-the-art level. These optical clocks could further be used to explore geophysical phenomena10, detect gravitational waves11, test general relativity12 and search for dark matter13-17.

Multivariate statistical analysis for selecting optimal descriptors in the toxicity modeling of nanomaterials.

The present study is based on the application of a multivariate statistical analysis approach for the selection of optimal descriptors of nanomaterials with the objective of robust qualitative modeling of their toxicity. A novel data mining protocol has been developed for the selection of an optimal subset of descriptors of nanomaterials by using the well-known multivariate method principal component analysis (PCA). The selected subsets of descriptors were validated for qualitative modeling of the toxicity of nanomaterials in the PC space. The analysis and validation of the proposed schemes were based on five decisive nanomaterial toxicity data sets available in the published literature. Optimal descriptors were selected on the basis of the maximum loading criteria and using a threshold value of cumulative variance ≤90% on PC directions. A maximum inter-class separation(B) and the minimum intra-classes separation(A) were obtained for toxic vs. nontoxic nanomaterials in the PC space with the selected subsets of optimal descriptors compared to their other combinations for each of the datasets.

Faraday-Shielded dc Stark-Shift-Free Optical Lattice Clock.

We demonstrate the absence of a dc Stark shift in an ytterbium optical lattice clock. Stray electric fields are suppressed through the introduction of an in-vacuum Faraday shield. Still, the effectiveness of the shielding must be experimentally assessed. Such diagnostics are accomplished by applying high voltage to six electrodes, which are grounded in normal operation to form part of the Faraday shield. Our measurements place a constraint on the dc Stark shift at the 10^{-20} level, in units of the clock frequency. Moreover, we discuss a potential source of error in strategies to precisely measure or cancel nonzero dc Stark shifts, attributed to field gradients coupled with the finite spatial extent of the lattice-trapped atoms. With this consideration, we find that Faraday shielding, complemented with experimental validation, provides both a practically appealing and effective solution to the problem of dc Stark shifts in optical lattice clocks.

Template-free synthesis of monolithic carbon xerogels with hierarchical porosity from resorcinol and formaldehyde via hydrothermal reaction.

Monolithic carbon xerogels with hierarchical porosity were prepared from resorcinol (R) and formaldehyde (F) via a base-catalysed hydrothermal polycondensation reaction, without a template and supercritical drying. First, an aqueous solution of resorcinol, formaldehyde and sodium carbonate was prepared by varying R/W (25-45) and R/C (1-10k) ratios to produce monolithic RF gels. The reaction was carried out in a pressurized Teflon mould at 100 °C for 6 h to give a co-continuous pore structure via spinodal decomposition and a tenacious gel to avoid supercritical drying. Next, the RF gels were dried for 42 h at 60 °C and another 6 h at 100 °C to produce RF xerogels without cracks, followed by pyrolysis in a tube furnace at 900 °C for 2 h under N2 flow, and then activation at 1000 °C for 2, 4 or 6 h under CO2 flow. Finally, the carbon xerogels were characterized by SEM and N2 adsorption-desorption measurements. Monolithic RF gels were obtained from all combinations of R/W and R/C, but the gels from R/W = 45 exhibited a co-continuous large-pore structure, providing a specific surface area (SSA) of ∼650 m2 g-1, which increased to 3311 m2 g-1 (for R/C = 10k) at 6 h of CO2 activation without exhibiting cracks. N2 isotherms demonstrated that micro- and meso-pores were introduced via activation, forming hierarchical porosity in combination with large pores from spinodal decomposition without using a template.

Development of Theoretical Descriptors for Cytotoxicity Evaluation of Metallic Nanoparticles.

Motivated by the recent development of quantitative structure-activity relationship (QSAR) methods in the area of nanotoxicology, we proposed an approach to develop additional descriptors based on results of first-principles calculations. For the evaluation of the biochemical activity of metallic nanoparticles, we consider two processes: ion extraction from the surface of a specimen to aqueous media and water dissociation on the surface. We performed calculations for a set of metals (Al, Fe, Cu, Ag, Au, and Pt). Taking into account the diversity of atomic structures of real metallic nanoparticles, we performed calculations for different models such as (001) and (111) surfaces, nanorods, and two different cubic nanoparticles of 0.6 and 0.3 nm size. Significant energy dependence of the processes from the selected model of nanoparticle suggests that for the correct description we should combine the calculations for several representative models. In addition to the descriptors of chemical activity of the metallic nanoparticles for the two studied processes, we propose descriptors for taking into account the dependence of chemical activity from the size and shape of nanoparticles. Routes to minimization of computational costs for these calculations are also discussed.

Hyperpolarizability and Operational Magic Wavelength in an Optical Lattice Clock.

Optical clocks benefit from tight atomic confinement enabling extended interrogation times as well as Doppler- and recoil-free operation. However, these benefits come at the cost of frequency shifts that, if not properly controlled, may degrade clock accuracy. Numerous theoretical studies have predicted optical lattice clock frequency shifts that scale nonlinearly with trap depth. To experimentally observe and constrain these shifts in an ^{171}Yb optical lattice clock, we construct a lattice enhancement cavity that exaggerates the light shifts. We observe an atomic temperature that is proportional to the optical trap depth, fundamentally altering the scaling of trap-induced light shifts and simplifying their parametrization. We identify an "operational" magic wavelength where frequency shifts are insensitive to changes in trap depth. These measurements and scaling analysis constitute an essential systematic characterization for clock operation at the 10^{-18} level and beyond.

Trans-tensor tympani facial nerve decompression in traumatic facial nerve palsy.

OBJECTIVE: The surgical approaches previously reported for facial nerve decompression have focussed on achieving good exposure of the lateral or superior aspects of the geniculate ganglion. This report aims to describe a unique case of facial nerve decompression beneath the geniculate ganglion. PATIENT: A 30-year-old woman with right-sided facial palsy due to a temporal bone fracture. INTERVENTION: Bony fragments at the base of the geniculate ganglion were removed via a trans-tensor tympani approach with extended posterior tympanotomy. RESULTS: The patient's facial movement recovered successfully, without complications such as sensorineural hearing loss and conductive hearing loss. CONCLUSION: In rare cases requiring decompression of the facial nerve inferior to the perigeniculate area, the trans-tensor tympani approach should be considered as a valuable alternative option when surgical intervention is considered.

Coenzyme Q10 in combination with steroid therapy for treatment of sudden sensorineural hearing loss: a controlled prospective study.

OBJECTIVE: To evaluate the therapeutic efficacy of coenzyme Q10 added to systemic steroid in patients with idiopathic sudden sensorineural hearing loss. DESIGN: A controlled prospective study. SETTING: Asan medical center, University of Ulsan College of Medicine. PARTICIPANTS: Between August 2007 and October 2008, the first 60 patients diagnosed with sudden sensorineural hearing loss were managed with systemic steroid treatment for 2 weeks including 5-day hospitalisation. And the second 60 patients were managed with coenzyme Q10 for 2 weeks added to previous management. MAIN OUTCOME MEASURES: We evaluated auditory function by pure tone audiometry and speech discrimination score. Auditory evaluations were performed before and 3 months after treatment using Siegel's criteria. The degree of improvement in four-tone average hearing and speech discrimination score was calculated from the results before and after treatment. RESULTS: The total hearing improvement rate after the treatment was 75.0% (90/120 patients) in this study. Although 47 patients (78.3%) of coenzyme Q10 group showed better hearing improvement than 43 patients (71.7%) of control group, there was no significant difference. However, the coenzyme Q10 group showed significantly higher improvement in speech discrimination score. CONCLUSION: From this study, we suggest that coenzyme Q10 may have beneficial effects in the treatment of sudden sensorineural hearing loss.

Polarization orthogonalizer for a pair of laser beams with nearly equal frequencies.

We have demonstrated a device to produce an overlapping pair of orthogonally polarized laser beams with a 3 GHz frequency offset out of a single laser beam containing the two frequency components with the same linear polarization. Our design is based on a Michelson interferometer formed by a polarizing beam splitter and two quarter-waveplates. Such a device can be used to make the polarization states of a carrier and a sideband produced through modulation mutually orthogonal. An orthogonally polarized pair of coherent laser beams can be used for an interferometric measurement of a small displacement in a heterodyne scheme or to produce a large-contrast coherent population trapping signal from alkali metal atoms. As a demonstration we used the device to achieve 40% contrast for a coherent population trapping signal from a rubidium vapor cell.

Lipo-prostaglandin E1 in combination with steroid therapy is effective for treatment of sudden sensorineural hearing loss in Korean patients with Type 2 diabetes.

BACKGROUND: Diabetes mellitus is a risk factor for sudden sensorineural hearing loss (SSNHL), possibly as a result of microvascular damage, increased blood viscosity and embolic and thrombotic episodes. Aim To perform a prospective, randomized clinical trial to determine the therapeutic effect of lipo-prostaglandin E(1) (lipo-PGE(1)) on SSNHL in Korean patients with Type 2 diabetes. METHODS: The study group consisted of 270 consecutive Korean patients (130 male, 140 female) in whom SSNHL was diagnosed. Patients were classified as diabetic or non-diabetic by the new American Diabetes Association criteria. With the approval of the institute ethics committee, patients were randomly assigned to treatment with of 10 microg lipo-PGE(1) (lipo-PGE(1) group) given as a continuous infusion over 5 days, or saline (placebo group). In addition, all patients studied were treated with 48 mg methylprednisolone for 5 days. RESULTS: The overall recovery rates after treatment were 51.5% in diabetic and 64.2% in non-diabetic patients. In diabetic patients, there was a significantly higher rate of hearing improvement in the lipo-PGE(1) group (64.7%) compared with the placebo group (37.5%), whereas, in non-diabetic patients, there was no significant difference in rate of hearing improvement between the lipo-PGE(1) group (70.3%) and the placebo group (58.3%). CONCLUSION: Lipo-PGE(1) may have beneficial effects in the treatment of SSNHL in Korean patients with Type 2 diabetes.

Sweep optical frequency synthesizer with a distributed-Bragg-reflector laser injection locked by a single component of an optical frequency comb.

A sweep optical frequency synthesizer is demonstrated by using a frequency-stabilized optical frequency comb and injection-locked distributed-Bragg-reflector (DBR) laser diode. The injection-locked DBR laser acts as a single-frequency filter and, simultaneously, a high-gain amplifier of the optical frequency comb. The frequency instability of the heterodyne beat signal between two independently injection-locked DBR lasers is measured to be 2.3 x 10(-16) at 1 s averaging time. The output frequency of the sweep optical frequency synthesizer can be precisely tuned over 1 GHz, and a saturated absorption spectrum of the Cs D2 line at 852 nm is recorded by the injected DBR laser.

Effects of salicylic-lactic acid conditioner on the shear bond strength of brackets and enamel surfaces.

The purpose of this study was to evaluate the effects of salicylic-lactic (SL) acid conditioner on the shear bond strength of brackets. Fluoride releasing (Light-bond) and non-fluoride releasing (Enlight) composite adhesives were used after conditioning with 0.22% salicylic + 9% lactic acid or 34% phosphoric acid. Composite adhesives were light cured with either a halogen light curing (HLC) unit for 30-50 s or a plasma arc curing (PAC) unit for 4 s. The shear bond strength was measured with an Instron. Failure modes of debonded brackets were identified based on adhesive remnants on the bracket and tooth. Salicylic-lactic acid conditioning was found to provide adequate shear bond strength. Groups conditioned with SL acid were debonded mainly at the enamel-resin interface and comparatively clean enamel surface after debonding was observed than those conditioned with phosphoric acid. Using confocal laser scanning microscopic examinations, it was found that demineralization patterns between SL acid and phosphoric acid conditioned groups were not different when the same adhesive was used. The SL acid conditioner did not reduce the demineralization. Light-bond adhesive showed less demineralization than Enlight adhesive. The PAC unit can be recommended as an alterative to the HLC unit because it significantly reduces the irradiation time.

Effect of plasma arc curing on polymerization shrinkage of orthodontic adhesive resins.

The purpose of this study was to evaluate the polymerization shrinkage of three orthodontic adhesive resins when polymerized with a high-energy plasma arc light (1340 mW cm(-2)) and a conventional halogen light (500 mW cm(-2)), and to correlate the polymerization shrinkage with the degree of conversion. To equalize the total light energy delivered to the adhesive resin, irradiation time was varied between 3 or 6 s for a plasma arc-curing unit, and 8 or 16 s for a halogen light-curing unit. The polymerization shrinkage of adhesive resins during the light-curing process was measured using a computer-controlled mercury dilatometer and the degree of conversion was measured using Fourier transform infrared spectroscopy. A plasma arccuring unit produced significantly lower polymerization shrinkage than a halogen light-curing unit when the equivalent total light energy was irradiated to the orthodontic adhesive resins (P < 0.05). The magnitude of polymerization shrinkage was significantly different depending on the kind of adhesive resins (P < 0.05), but there was no significant correlation between the filler fraction and the polymerization shrinkage (r2 = 0.039). There was strong correlation (r2 = 0.787) between the polymerization shrinkage and the degree of conversion with a halogen light-curing unit, but poor correlation (r2 = 0.377) was observed with a plasma arc-curing unit.

Degree of polymerization of resin composites by different light sources.

The purpose of this study was to determine the effectiveness of polymerization in the newly introduced blue light emitting diode (LED) (Experimental, SNU, Korea), and plasma arc curing (PAC) (Apollo 95E, Elite, DMD, USA) compared with conventional halogen lamp (Spectrum 800, Dentsply, USA). Various irradiation time with fixed intensity of light-curing units (LCUs) were irradiated to produce the same total light energy. The degree of double bond conversion (DC) of three resin composite (shade A3) was measured with a Fourier-transform infrared (FT-IR) spectrophotometer at various depths from the surface. Immediately after exposure to light, 100 microm thickness of resin composite was sectioned at the 1, 2, 3 and 4 mm from the top surface. The infrared spectrum of uncured resin and each wafer specimen were then obtained. The results were as follows: DC was significantly influenced by three variables of material, depth from the surface, and light source and energy level (P < 0.01). When the same light energy was irradiated, DC by plasma arc and LED was not significantly different from the halogen lamp (P > 0.05). When light energy was increased twice, no significant difference in DC was observed up to 2 mm from the surface (P > 0.05), but DC increased significantly from 3 mm (P < 0.05).

Effects of colour measuring mode and light source on the colour of shade guides.

The objectives of this paper were to evaluate the effects of colour measuring modes [specular component excluded (SCE) versus specular component included (SCI)] and the standard light source (C, A or D65) on the colour of shade guides. After the labial part of shade tabs of two shade guides (Vita and Chromascop) was polished flat up to no. 2400 silicone carbide paper, the colour was measured according to the International Commission on Illumination (CIE)L*a*b* colour scale on a spectrophotometer. In both shade guides, all the average CIE L* values of each shade series, and most of CIE b* values were different depending on the measuring mode (P < 0.01). However, there was no difference in CIE a* values depending on the measuring mode. Colour difference (deltaE*) between the values measured with SCE mode and with SCI mode was 3.21-6.50 in Vita shade guide, 3.22-5.47 in Chromascop shade guide. DeltaE* caused by the difference in light source was very small in Vita shade guide regardless of the measuring mode. In the Vita shade guide, the shade series (A-D) was negatively correlated with CIE L* and CIE a* values measured with SCE mode. In the Chromascop shade guide, the shade series (100-500) was negatively correlated with CIE L* value measured with SCI mode.

The relationship between body mass index and the prevalence of obesity-related diseases based on the 1995 National Health Interview Survey in Korea.

This study estimated the body mass index (BMI) distribution of Koreans and examined the relationship between BMI and obesity-related diseases, in particular hypertension and diabetes mellitus. We also attempted to provide primary data to determine suitable BMI cut-off points for obesity in Korea. The 1995 National Health Interview Study (NHIS) data were used to estimate BMI and the prevalence of hypertension and diabetes mellitus. A random sample of 5750 Koreans (15-69 years of age) were investigated. BMI was calculated by self-reported weights and heights. The diagnoses of hypertension and diabetes mellitus were obtained from self-reported conditions specified in response to consultations with physicians. The mean BMI was 22.6+/-2.6 kg m(-2) for males and 21.7+/-4.8 kg m(-2) for females. The prevalence of hypertension and diabetes mellitus increased with BMI. The odds ratios of the third quartile of BMI (21.9-23.8 kg m(-2)) for hypertension and diabetes mellitus compared with the first quartile were 6.04 and 3.22, respectively. The odds ratio of the fourth quartile (>23.8 kg m(-2)) of BMI was not significantly different from that of the third quartile. The risk of hypertension and diabetes mellitus increased at the third quartile of BMI (21.9-23.8 kg m(-2)), this quartile being much lower than both the current World Health Organization (WHO) BMI cut-off point of overweight of 25.0 kg m(-2), and the 90th percentile proposed in the Monica project, BMI 26.4 kg m(-2). This finding was notable considering the fact that both hypertension and diabetes mellitus occur in Koreans with lower BMIs than whites. Further studies are necessary to identify the BMI cut-off point for obesity in Korea.

Inhibition of cholesteatomatous bone resorption with pamidronate disodium.

Bone destruction is known to be an important cause of complications in chronic cholesteatomatous otitis media. A strategy that blocks localized bone resorption may prevent the progression of the disease. The bisphosphonate drug pamidronate is known to inhibit bone resorption and has been used in the treatment of Paget's disease and osteoporosis. The aim of this study was to investigate the effect of pamidronate on the inhibition of bone resorption in cholesteatoma using a neonatal rat calvarial culture system. Radioactive calcium was subcutaneously injected into pregnant rats. Neonatal calvariae were harvested after i.p. injection of pamidronate disodium to neonatal rats and culture supernatants of cholesteatoma keratinocytes were then added to the calvarial culture media. Radioactive calcium release was measured using a beta-ray scintillation counter. The percentage of calcium release was significantly higher in cholesteatoma culture supernatant than in Dulbecco's modification of Eagle's medium. The percentage calcium release in cholesteatoma culture supernatant was significantly lower with the high dose of pamidronate than with the low dose. These results suggest that pamidronate can inhibit the bone resorption caused by cholesteatoma. This study suggests a possible application for pamidronate in the prevention of cholesteatomatous bone destruction.

A micromachined silicon depth probe for multichannel neural recording.

A process of making a new type of silicon depth-probe microelectrode array is described using a combination of plasma and wet etch. The plasma etch, which is done using a low temperature oxide (LTO) mask, enables probe thickness to be controlled over a range from 5 to 90 mu. Bending tests show that the probe's mechanical strength depends largely on shank thickness. More force can be applied to thicker shanks while thinner shanks are more flexible. One can then choose a thickness and corresponding mechanical strength using the process developed. The entire probe shaping process is performed only at low temperature, and thus is consistent with the standard CMOS fabrication. Using the probe in recording from rat's somatosensory cortex, we obtained four channel simultaneous recordings which showed clear independence among channels with a signal-to-noise ratio performance comparable with that obtained using other devices.

Salivary gland choristoma of the middle ear: a case report.

A choristoma is a nonneoplastic proliferation of histologically normal tissue that forms at an abnormal site. It is extremely uncommon in the middle ear space. It appears to be a developmental abnormality and may be associated with abnormalities of adjacent structures. It usually occurs with unilateral conductive hearing loss and requires a differential diagnosis from other mass lesions in the middle ear cavity. This article discusses a case of salivary gland choristoma of the middle ear that we believe to be the 24th case reported on this subject.

Nontwist quarter-wave liquid-crystal cell for a high-contrast reflective display.

We propose an optical configuration of a nontwist quarter-wave liquid-crystal cell for a high-contrast reflective display that can be applied to most nontwist display modes. By fabricating a homogeneous cell with the proposed configuration, we have demonstrated a high contrast ratio of 50:1 without using a wideband retardation film.