Search

We present this unusual fracture in order to stress the importance of being aware of the existence of open fractures of patella in 2-year-old child. Fractures of the patella are rare in children, as the patella is largely cartilaginous and has great mobility. Normally in this age closed patellar fractures cannot be diagnosed radiologically as the ossification starts only after 3 years of age. Our case is an open transverse patellar fracture in a two-year-old girl which is treated with transcartilagenous absorbable sutures, which is not found reported in the literature.

Cs2Hg3S4 was synthesized by slowly cooling a melted stoichiometric mixture of Hg and Cs2S4. Cs2Hg3S4 crystallizes in the Ibam spacegroup with a = 6.278(1) A, b = 11.601(2) A, and c = 14.431(3)A; dcalc = 6.29 g/cm3. Its crystal structure consists of straight chains of [Hg3S4]n2n– that engage in side-by-side weak bonding interactions forming layers and are charge balanced by Cs+ cations. The thermal stability of this compound was investigated with differential thermal analysis and temperature dependent in situ synchrotron powder diffraction. The thermal expansion coefficients of the a, b, and c axes were assessed at 1.56 × 10–5, 2.79 × 10–5, and 3.04 × 10–5 K–1, respectively. Large single-crystals up to ∼5 cm in length and ∼1 cm in diameter were grown using a vertical Bridgman method. Electrical conductivity and photoconductivity measurements on naturally cleaved crystals of Cs2Hg3S4 gave resistivity ρ of ≥108 Ω·cm and carrier mobility-lifetime (μτ) products of 4.2 × 10–4 and 5.82 × 10–5 cm2 V–1 for electro...

Cesium hydrogen l-malate monohydrate, CsH(C4H4O5)·H2O, is a new chiral open-framework semi-organic crystalline material with a second-harmonic generation efficiency one order of magnitude greater than KDP. Single crystals of this new material have been grown by the conventional slow cooling technique from aqueous solution. Grown crystals display both platy and prismatic morphologies depending on the imposed supersaturation. Hardness values measured using Vickers hardness indenter show considerable anisotropy. The resistivity behavior at room temperature and above, places the crystal between an ionic conductor and a dielectric. The single-crystal SHG efficiency estimated through Maker fringes experiment gives deff which is 4.24 times that of KDP. Single and multiple shot experiments performed on the grown crystals for the fundamental and second harmonic of pulsed Nd:YAG laser (1064 and 532 nm) show that it exhibits a high laser damage threshold which is a favorable property for nonlinear optical applications.

Laser-induced photoacoustic technique in the closed cell configuration has been employed to study the anisotropy in thermal parameters of urea L-malic acid, a nonlinear optical crystal. Thermal diffusivity values of the specimen along different crystallographic axes are evaluated from the measured amplitude and phase spectra of photoacoustic signal using one-dimensional model of Rosencwaig and Gersho. Thermal conductivity of the crystal along different axes is calculated using the measured thermal diffusivity and specific heat values. The measured thermal parameters are correlated with mechanical hardness as well as the bonding scheme of the crystal. Analyses of the results show that there is considerable anisotropy in heat diffusion parameters along different crystal orientations. Results are explained on the basis of crystallographic structure and the phonon-assisted heat diffusion mechanism in crystals.

A new nonlinear optical organic crystal, viz. Urea L-Malic acid, has been grown from aqueous solution employing the techniques of solvent evaporation and slow cooling. The grown crystals were found to be transparent in the visible region. The complete morphology of the crystal has been worked out and its hardness was evaluated using Vickers indentation method. The grown crystals were characterized employing several techniques such as micro-carbon-hydrogen-nitrogen analysis, X-ray diffraction, thermogravimetric analysis, differential thermal analysis, UV-VIS-IR spectroscopy and refractive index measurement. Preliminary measurements indicate that the second harmonic generation efficiency at a fundamental wavelength of 1064 nm is roughly three times that of KDP.

We report synchrotron radiation diffraction and muon spin rotation (muSR) measurements on the frustrated pyrochlore magnet Tb2Ti2O7. The powder diffraction study of a crushed crystal fragment does not reveal any structural change down to 4 K. The muSR measurements performed at 20 mK on a mosaic of single crystals with an external magnetic field applied along a three-fold axis are consistent with published a.c. magnetic-susceptibility measurements at 16 mK. While an inflection point could be present around an internal field intensity slightly above 0.3 T, the data barely support the presence of a magnetization plateau., Comment: To appear in the proceedings of the 13th International Conference on Muon Spin Rotation, Relaxation and Resonance, Grindelwald, Switzerland, 1-6 June 2014

The nature of the low-temperature ground state of the pyrochlore compound Tb${}_{2}$Ti${}_{2}$O${}_{7}$ remains a puzzling issue. Dynamic fluctuations and short-range correlations persist down to 50 mK, as evidenced by microscopic probes. In parallel, magnetization measurements show irreversibilities and glassy behavior below 200 mK. We have performed magnetization and ac susceptibility measurements on four single crystals down to 57 mK. We did not observe a clear plateau in the magnetization as a function of field along the [111] direction, as suggested by the quantum spin ice model. In addition to a freezing around 200 mK, slow dynamics are observed in the ac susceptibility up to 4 K. The overall frequency dependence cannot be described by a canonical spin-glass behavior.

The terahertz (THz) excitations in the quantum spin-ladder system Sr14Cu24O41 have been determined along the c axis using THz time-domain, Raman, and infrared spectroscopy. Low-frequency infrared and Raman active modes are observed above and below the charge-ordering temperature T(co) is approximately equal to 200 K over a narrow interval approximately equal to 1-2 meV approximately equal to 8-16 cm(-1)). A new infrared mode at approximately equal to 1 meV develops below approximately equal to 100 K. The temperature dependence of these modes shows that they are coupled to the charge- and spin-density-wave correlations in this system. These low-energy features are conjectured to originate in the gapped sliding motion of the chain and ladder subsystems, which are both incommensurate and charged.

The insulator pyrochlore Tb${}_{2}$Ti${}_{2}$O${}_{7}$ is a three-dimensional spin liquid candidate: the strength of the magnetic interaction would normally induce order at $\ensuremath{\approx}$20 K, but according to published muon-spin relaxation and neutron diffraction measurements, it is still in a correlated paramagnetic state down to a temperature of 0.05 K. Our detailed experimental investigation shows that an exotic transition takes place at ${T}_{\mathrm{t}}=0.15\phantom{\rule{0.16em}{0ex}}(2)$ K. It is characterized by an anomaly in the muon precession frequency shift but not in the specific heat, which nevertheless reveals the signature of degrees of freedom at very low energy. It might be associated with a cooperative Jahn-Teller transition. The robustness of the experimental results is discussed.

We report the direct observation by polarized inelastic neutron scattering experiments at low fields (3.5 T) of the splitting of the spin triplet of magnetic excitations in the response associated with the ladders in the composite cuprate Sr${}_{14}$Cu${}_{24}$O${}_{41}$. By conveniently choosing the magnetic field configuration and by making use of the spin chirality of the excitations, the splitting can be observed at relatively low fields. In this way, resonant excitations can be separated from the remainder of magnetic and phonon excitations at high temperatures. In Sr${}_{14}$Cu${}_{24}$O${}_{41}$, the 32-meV gapped mode vanishes above $~$200 K, close to the hole-crystal melting temperature previously observed by resonant x-ray and neutron diffraction.

The magnetic entropy variation for the ordered spin-ice Tb2Sn2O7 and the spin-liquid Tb2Ti2O7 measured up to similar to 20 K shows that the crystal-field ground state for both systems is a singlet split from the first excited level by a thermal energy of similar to 2 K. It is the superexchange interactions between the Tb3+ spins which induce the terbium magnetic moments. Our results are analyzed in terms of a tetragonal perturbation for Tb2Ti2O7 and this perturbation plus a molecular field for Tb2Sn2O7.

We report the direct observation by inelastic neutron scattering experiments of a spin triplet of magnetic excitations in the response associated with the ladders in the composite cuprate Sr14Cu24O41. This appears as a peak at q_{Q1D}=\pi and energy \Delta_1=32.5 meV, and we conjecture that all the triplets making up this conspicuous peak have the same phase and therefore interpret it as the signature of the occurrence of quantum coherence along the ladder direction between entangled spin pairs. From the comparison with previous neutron and x-ray data, we conclude that the temperature evolution of this mode is driven by the crystallization of holes into a charge density wave in the ladder sublattice

We report the direct observation by inelastic neutron scattering experiments of a spin triplet of magnetic excitations in the response associated with the ladders in the composite cuprate Sr14Cu24O41. This appears as a peak at q(Q1D)=π and energy Δ1=32.5 meV, and we conjecture that all the triplets making up this conspicuous peak have the same phase and therefore interpret it as the signature of the occurrence of quantum coherence along the ladder direction between entangled spin pairs. From the comparison with previous neutron and x-ray data, we conclude that the temperature evolution of this mode is driven by the crystallization of holes into a charge density wave in the ladder sublattice.

We investigate magnetic excitations in the spin-ladder compound Sr14Cu24O41 using high-resolution Cu L-3 edge resonant inelastic x-ray scattering (RIXS). Our findings demonstrate that RIXS couples to two-triplon collective excitations. In contrast to inelastic neutron scattering, the RIXS cross section changes only moderately over the entire Brillouin zone, revealing high sensitivity also at small momentum transfers, allowing determination of the two-triplon energy gap as 100 +/- 30 meV. Our results are backed by calculations within an effective Hubbard model for a finite-size cluster, and confirm that optical selection rules are obeyed for excitations from this spherically symmetric quantum spin-liquid ground state.

Single crystals of Sr14−xCaxCu24O41 (x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr14Cu24O41 show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. Tc onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with Tc max=9.4 K and TN=5 K at 56 kbars.

We investigate magnetic excitations in the spin-ladder compound Sr_{14}Cu_{24}O_{41} using high-resolution Cu L_{3} edge resonant inelastic x-ray scattering (RIXS). Our findings demonstrate that RIXS couples to two-triplon collective excitations. In contrast to inelastic neutron scattering, the RIXS cross section changes only moderately over the entire Brillouin zone, revealing high sensitivity also at small momentum transfers, allowing determination of the two-triplon energy gap as 100 +/- 30 meV. Our results are backed by calculations within an effective Hubbard model for a finite-size cluster, and confirm that optical selection rules are obeyed for excitations from this spherically symmetric quantum spin-liquid ground state.

We report the surface laser damage threshold in sodium p-nitrophenolate dihydrate, a nonlinear optical crystal. The experiment is performed with a pulsed Nd:YAG laser in TEM00 mode. The single shot damage thresholds are 11.16 +/- 0.28GWcm(-2) and 1.25 +/- 0.02GWcm(-2) for 1064 nm and 532 nm laser wavelengths respectively. A close correlation between the laser damage threshold and mechanical hardness is observed. A possible mechanism of laser damage is discussed.

We have experimentally studied the effect of X-ray irradiation on the structural and dielectric properties of glycine phosphite (GPI) single crystal around its ferroelectric phase transition. While there was no appreciable change in the lattice parameters, a significant drop in the value of dielectric constant and tan \delta was observed upon irradiation. The peak value of dielectric constant reduced progressively with the exposure time. An appreciable shift in the phase transition temperature towards the lower temperature was observed. These changes in the structure and dielectric properties of GPI are attributed to the defects produced in it by irradiation. An electron paramagnetic resonance measurement of the irradiated sample revealed that the defect created is $PO_{3}^{2-}$ radical.

Sodium p-nitrophenolate dihydrate $(NPNa.2H_2O)$, is a semiorganic nonlinear optical crystal which is reported to have an effective nonlinear optical coefficient of 5 pm/V. The crystal is usually grown from methanol. By suitably varying the growth parameters, we obtained stable, transparent, sodium p-nitrophenolate dihydrate using water as a solvent. Large single crystals of the dimension $20 \times 17 \times 8 mm^3$were grown by a temperature-lowering method. Preliminary characterizations were carried out on the grown sample and compared with methanol-grown $NPNa.2H_2O$. The optical transmission study on these crystals revealed that the crystals grown from aqueous solution have a higher percentage of transmission, thereby favourably affecting optical performance.

Near-stoichiometric lithium niobate (SLN) crystals doped with up to 1.6 mol % Zn and codoped with various Nd concentrations in the melt (0.2, 0.5, 0.9, and 1.5 mol %) (Nd:Zn:SLN)are grown from 58.6 mol % $Li_2O$ using conventional Czochralski technique. Crystals are pulled at the rate of 0.35 mm/h with seed rotation at 9 rpm. Concentrations of Zn and Nd in the crystal are varied by adding appropriate amounts of ZnO and $Nd_2O_3$ to the starting composition. Unit cell parameters of the grown crystals are calculated by Rietveld refinement method using FULLPROFF software. Domain structure studies are carried out by chemical etching followed by microscopic examination. Dielectric studies reveal the existence of piezoelectric resonance at high frequencies. Enhancement in dielectric constant and $tan \delta$ in Nd doped samples has been attributed to the space charge polarization. Nd doped samples exhibit reduction in the relative permittivity after oxygen annealing. Transmission spectra of Nd:Zn:SLN crystals in the UV region exhibit blueshift in the cutoff wavelength. In Mid Infrared (MIR) region crystals doped with 1.6 mol % Zn have shift in the OH absorption peak from 2873 to 2833 nm. Judd–Ofelt analysis carried out on the absorption spectra of codoped crystal yields the lifetime of $104 \mu$ s for the metastable state $^4F_{3/2}$. The branching ratio for the electronic transition from $^4F_{3/2}$ to $^4I_{11/2}$ is high compared to that for $^4F_{3/2}$ to $^4I_{13/2}$, indicating a higher emission cross section for the former transition. Laser damage threshold evaluated using 532 nm, 5 ns pulsed neodymium doped yttrium aluminum garnet laser, shows an increase by two orders of magnitude for crystals doped with 1.6 mol % Zn. Photorefractive damage threshold for these crystals shows an enhancement of four orders of magnitude due to increase in the photoconductivity.

The effect of x-ray irradiation on polarization switching properties of a glycine phosphite (GPI) single crystal is investigated using the Merz technique. GPI undergoes a paraelectric to ferroelectric phase transition at 224.7 K. Switching studies were performed in the temperature range of 173–221 K with the applied field varying from 1.1 to 4.9 kV/cm. X-ray irradiation causes an increase in the threshold field below which switching could not occur. The activation energy for the domain wall motion is found to increase with irradiation from 0.12 eV for a pristine sample to 0.34 eV after irradiating it for 20 min. The temperature dependence of domain wall mobility shows an unusual behavior with the radiation dosage. The calculated domain wall mobility increases with the exposure time, which is contrary to expectation. This apparent increase in mobility with exposure time is attributed to the creation of a large number of radiation induced defects, identified as $PO_3^{2-}$ radicals, resulting in the loss of effective switchable volume of the sample.

A detailed study of surface laser damage performed on a nonlinear optical crystal, urea L-malic acid, using 7 ns laser pulses at 10 Hz repetition rate from a Q-switched Nd:YAG laser at wavelengths of 532 and 1064 nm is reported. The single shot and multiple shot surface laser damage threshold values are determined to be 26.64±0.19 and 20.60±0.36 GW cm−2 at 1064 nm and 18.44±0.31 and 7.52±0.22 GW cm−2 at 532 nm laser radiation, respectively. The laser damage anisotropy is consistent with the Vickers mechanical hardness measurement performed along three crystallographic directions. The Knoop polar plot also reflects the damage morphology. Our investigation reveals a direct correlation between the laser damage profile and hardness anisotropy. Thermal breakdown of the crystal is identified as the possible mechanism of laser induced surface damage.