Ultra-low-vibration closed-cycle cryogenic surface-electrode ion trap apparatus

We describe the design, commissioning, and operation of an ultra-low-vibration closed-cycle cryogenic ion trap apparatus. One hundred lines for low-frequency signals and eight microwave/radio frequency coaxial feed-lines offer the possibility of implementing a small-scale ion-trap quantum processor or simulator. With all supply cables attached, more than 1.3 W of cooling power at 5 K is still available for absorbing energy from electrical pulses introduced to control ions. The trap itself is isolated from vibrations induced by the cold head using a helium exchange gas interface. The performance of the vibration isolation system has been characterized using a Michelson interferometer, finding residual vibration amplitudes on the order of 10 nm rms. Trapping of ⁹Be⁺ ions has been demonstrated using a combination of laser ablation and photoionization.

Tumor regression grading after neoadjuvant treatment of esophageal and gastroesophageal junction adenocarcinoma: results of an international Delphi consensus survey

Complete histopathologic tumor regression after neoadjuvant treatment is a well-known prognostic factor for survival among patients with adenocarcinomas of the esophagus and gastroesophageal junction. The aim of this international Delphi survey was to reach a consensus regarding the most useful tumor regression grading (TRG) system that could represent an international standard for histopathologic TRG grading of gastroesophageal carcinomas. Fifteen pathologists with special interest in esophageal and gastric pathology participated in the online survey. The initial questionnaire contained of 43 statements that addressed the following topics: (1) specimen processing, (2) gross examination, (3) cross sectioning, (4) staining, (5) Barrett's esophagus, (6) TRG systems, and (7) TRG in lymph node (LN). Participants rated the items using a 5-point Likert style scale and were encouraged to write comments for each statement. The expert panel recommended a 4-tiered TRG system for assessing the primary tumor: grade 1: No residual tumor (complete histopathologic tumor regression), grade 2: less than 10% residual tumor (near-complete regression), grade 3: 10%-50% residual tumor (partial regression), grade 4: greater than 50% residual tumor (minimal/no regression), combined with a 3-tiered system for grading therapeutic response in metastatic LNs: grade a: no residual tumor (complete histopathologic TRG), grade b: partial regression (tumor cells and regression), grade c: no regression (no sign of tumor response). This TRG grading system can be recommended as an international standard for histopathologic TRG grading in esophageal and gastroesophageal junction adenocarcinoma.

Deformation-Induced Chemical Inhomogeneity and Short-Circuit Diffusion in Shear Bands of a Bulk Metallic Glass

The compositional changes in shear bands of a Cu_{50}Zr_{50} metallic glass after plastic deformation at room temperature have been monitored by atom probe tomography. Across the width of the shear bands an asymmetry of the enriched and depleted zones of the constituent elements is observed, while no change of the composition within the surrounding matrix occurs. The diffusion coefficients determined from the concentration profiles are orders of magnitude larger than the values of bulk diffusion at room temperature. The asymmetric concentration profiles of the constituent elements (Cu and Zr) remain stable during annealing at a temperature of 543 K, even though fast and preferential diffusion of a Ni tracer has been found along the shear band at the same temperature. The results indicate that the atomic structure and stress distribution within the shear bands is altered from that of the surrounding amorphous matrix. The fact that the shear band structure is unaltered at elevated temperatures and that fast diffusion occurs preferentially within the shear bands leads to the conclusion that they are structurally stable.

Robust and Resource-Efficient Microwave Near-Field Entangling ^{9}Be^{+} Gate

Microwave trapped-ion quantum logic gates avoid spontaneous emission as a fundamental source of decoherence. However, microwave two-qubit gates are still slower than laser-induced gates and hence more sensitive to fluctuations and noise of the motional mode frequency. We propose and implement amplitude-shaped gate drives to obtain resilience to such frequency changes without increasing the pulse energy per gate operation. We demonstrate the resilience by noise injection during a two-qubit entangling gate with ^{9}Be^{+} ion qubits. In the absence of injected noise, amplitude modulation gives an operation infidelity in the 10^{-3} range.

Versatile Control of ^{9}Be^{+} Ions Using a Spectrally Tailored UV Frequency Comb

We demonstrate quantum control of ^{9}Be^{+} ions directly implemented by an optical frequency comb. Based on numerical simulations of the relevant processes in ^{9}Be^{+} for different magnetic field regimes, we demonstrate a wide applicability when controlling the comb's spectral properties. We introduce a novel technique for the selective and efficient generation of a spectrally tailored narrow-bandwidth optical frequency comb near 313 nm. We experimentally demonstrate internal state control and internal-motional state coupling of ^{9}Be^{+} ions implemented by stimulated-Raman manipulation using a spectrally optimized optical frequency comb. Our pulsed laser approach is a key enabling step for the implementation of quantum logic and quantum information experiments in Penning traps.

Modifying the transition temperature, 120 K ≤ Tc ≤ 1150 K, of amorphous Fe90-xCoxSc10 with simultaneous alteration of fluctuation of exchange integral up to zero

Amorphous (a-) Fe_90−xCo_xSc₁₀ alloys have been produced by rapid quenching from the melt. The Curie temperature, T_C, was determined using both mean field theory and Landau’s theory of second-order phase transitions in zero and non-zero external fields. The dependence of T_C on the atomic spacing can be explained by the empirical Bethe-Slater curve. The value of T_C of a- Fe₅Co₈₅Sc₁₀, determined by the above theoretical approaches is 1150 K, which is the highest T_C ever measured for amorphous alloys. The flattening of the measured normalized magnetization, M(T)/M(0), as a function of the reduced temperature, T/T_C, is explained within the framework of the Handrich- Kobe model. According to this model the fluctuation of the exchange integral is the main reason for the flattening of M(T)/M(0). In the case of a-Fe₉₀Sc₁₀ without Co, however, the fluctuation of the exchange integral is dominant only at zero external field, B_ex = 0. At B_ex = 9 T, however, the fluctuation of the exchange integral has no conspicuous effect on the reduction of the magnetization. It is shown that at B_ex = 9 T the frozen magnetic clusters control the behaviour of the reduced magnetization as function of T/T_C. In contrast to other ferromagnetic alloys, where the flattening of M(T)/M(0) is characteristic for an amorphous structure, the a- Fe₅Co₈₅Sc₁₀ does not exhibit any trace of the fluctuation of the exchange integral.

Electrical resistivity and wave character of free electrons in amorphous and nanoglass Sc75Fe25

The residual electrical resistivity of metallic amorphous alloys, ρ ₀, is typically in the range 50 µΩ cm  <  ρ ₀  <  310 µΩ cm corresponding to a mean free path of conduction electrons of order a few interatomic distances. In crystalline metals with low defect levels such as Cu however, the residual electrical resistivity is about ρ ₀  ≈  1.54  ×  10^-2 µΩ cm, leading to extensive progression of free electrons through the crystalline material, of typically up to 4  ×  10⁶ nm. The relatively 'high' values for the electrical resistivity of distorted Sc₇₅Fe₂₅ alloys are discussed here within the framework of the wave character of electrons. The present investigation of amorphous and nanoglass Sc₇₅Fe₂₅ over the temperature range 1.9-320 K, focuses on clarification of the temperature dependence of the resistivity, ρ(T). These alloys systems, which show a range of behaviours for temperature dependent resistivity-including temperature independent residual resistivity, as well as positive and negative polarities for the slope dρ(T)/dT-are examined in detail.

Cervical cord and ventricle affection in neuromyelitis optica

OBJECTIVES

Cervical cord involvement is common in neuromyelitis optica (NMO) and multiple sclerosis (MS), but its impact on disability in NMO has rarely been studied. Recent publications on NMO examined the periventricular system, areas of high aquaporin-4 expression, but not yet by using ventricle volumetry.

PURPOSE

To compare cervical cord atrophy, ventricular widening, and supra- and infratentorial brain measures between NMO and MS, and study their impact on clinical disability.

METHODS

Magnet resonance imaging-based volumetry of upper cervical cord, third and fourth lateral ventricles, grey matter, white matter, brainstem, cerebellum and clinical status of 18 NMO and 20 MS patients, was compared between the groups and with 26 healthy controls. Patterns of ventricular widening relative to healthy controls were inspected by voxel-based morphometry of the cerebrospinal fluid.

RESULTS

Cervical cord atrophy was similar in NMO and MS (75.2 ± 10.0 mm² , respectively, 76.5 ± 9.5 mm² vs 84.1 ± 8.6 mm² in controls).Third ventricle increase in both groups, and specific fourth ventricle widening in MS were detected. Patient groups differed in third to fourth ventricle ratio (P = 0.002). In NMO, white matter correlated inversely with the affected cord segments (P = 0.001) and with cervical cord area (P = 0.043). The disability status was explained by cervical cord area and third ventricle volume (R² =0.524) in NMO, and by grey matter and fourth ventricle volume (R² =0.565) in MS.

CONCLUSION

Cervical cord atrophy and third ventricular enlargement are both clinically relevant in NMO. Third and fourth ventricle volumetry shows differences between NMO and MS regarding the involvement of periventricular structures.

Identification of a genetic contamination in a commercial mouse strain using two panels of polymorphic markers

Rapid detection of genetic contamination is critical in mouse studies involving inbred strains. During a Quantitative Trait Locus (QTL) study using simple sequence length polymorphism (SSLP) markers, we noticed heterozygosity at some loci of a commercially available inbred C57BL/6N mouse strain, suggesting a contamination by another mouse strain. A panel of 100 single-nucleotide polymorphism (SNP) markers was used to confirm and specify the genetic contamination suspected. Retrospective analyses demonstrated that the contamination took place as early as autumn 2003 and has persisted ever since at a fairly constant level. Contaminating alleles most probably originated from a DBA strain. Our data demonstrate the suitability of SNP markers for rapid detection and identification of the source of genetic contamination. Further, our results show the importance of a state-of-theart genetic monitoring of the authenticity of murine inbred strains.

The truth about the 1st cycle Coulombic efficiency of LiNi1/3Co1/3Mn1/3O2 (NCM) cathodes

High voltage issues of the NCM cathode could be attributed predominantly to structural instabilities and unexpected negligible electrolyte oxidation.

Hedgehog/Patched-associated rhabdomyosarcoma formation from delta1-expressing mesodermal cells

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma. In children, the 2 major RMS subtypes are alveolar and embryonal RMS. Aberrant Hedgehog/Patched1 (Hh/Ptch) signaling is a hallmark of embryonal RMS. We demonstrate that mice carrying a Ptch mutation in mesodermal Delta1-expressing cells develop embryonal-like RMS at a similar rate as mice harboring a Ptch mutation in the germline or the brachury-expressing mesoderm. The tumor incidence decreases dramatically when Ptch is mutated in Myf5- or Pax3-expressing cells. No RMS develop from Myogenin/Mef2c-expressing cells. This suggests that Hh/Ptch-associated RMS are derived from Delta1-positive, Myf5-negative, Myogenin-negative and Pax3-negative mesodermal progenitors that can undergo myogenic differentiation but lack stable lineage commitment. Additional preliminary genetic data and data on mesodermal progenitors further imply an interplay of Hh/Ptch and Delta/Notch signaling activity during RMS initiation. In contrast, Wnt signals supposedly suppress RMS formation because RMS multiplicity decreases after inactivation of the Wnt-inhibitor Wif1. Finally, our results strongly suggest that the tumor-initiating event determines the lineage of RMS origin.

Controlling spin polarized band-structure by variation of vacancy intensity in nanostructures

In this study, the magnetic properties of FeAl alloys with different grain sizes produced by high-pressure torsion were probed by means of magnetic Compton scattering. The measurements were performed at 300 and 10 K. Magnetic Compton profiles of nanocrystalline (35 nm) and ultrafine-grained (160 nm) FeAl alloys were analyzed in terms of the integral area, the width, and the distinctive dip intensity at low momenta. The changes in total magnetic moment and the strength of spin-polarization of itinerant electrons are assumed to be caused by vacancies induced during the preparation of the samples. Despite local disordering due to interfacial regions and deviations in perfect stoichiometry for B2 structure, the effect of vacancies is considered as the major magnetic state contributor.

Normal values for transbulbar sonography and magnetic resonance imaging of the optic nerve sheath diameter (ONSD) in children and adolescents

PURPOSE

To establish normal values of the optic nerve sheath diameter (ONSD) in children and adolescents for transbulbar sonography and magnetic resonance imaging.

MATERIALS AND METHODS

In 99 children and adolescents (age: 5.6 - 18.6 years, mean: 12 years) without neurologic or ophthalmologic disease, measurements of the ONSD with transbulbar sonography were performed. For comparison 59 children and adolescents (age: 5.1 - 17.4 years, mean 12.3 years) with a normal MR examination of the brain had measurements of the ONSD on a T2-weighted thin section sequence of the orbit. Besides establishing modality-related normal values, age dependency, accuracy and reproducibility of measurements were assessed.

RESULTS

Overall the mean ONSD was 5.75 ± 0.52 mm for transbulbar sonography and 5.69 ± 0.31 mm for MRI. There was no statistical significance between the 95 % percentiles and age for both transbulbar sonography (p = 0.332) and MRI (p = 0.336). As a parameter for the reproducibility of measurements, the repeatability coefficient (RC) was between 0.34 mm and 0.46 mm. The concordance correlation coefficient (CCC) values revealed a high agreement between readers both for transbulbar sonography (0.868) and MRI (0.796).

CONCLUSION

Normal values for ONSD in children and adolescents found in this study are significantly higher than assumed. The values found for transbulbar sonography are confirmed by comparable results for MR measurements. A precise sonographic measurement technique and the consideration of normal values found hereby are essential for correct interpretation of ONSD measurements in children and adolescents.

A versatile apparatus for the fine-tuned synthesis of cluster-based materials

In this paper, a custom-designed experimental setup for the fine-tuned synthesis of various cluster-based materials is presented. Providing custom-designed deposition stages and special sample holders it offers a high degree of control over the sample characteristics such as the cluster size, cluster amounts, and sample homogeneity in combination with high sample purity. The system is capable of producing thin films of pure clusters and various cluster-matrix combinations with cluster sizes ranging from single atoms up to aggregates of several thousand atoms. Two custom-designed deposition stages are available, one utilizes the full cluster beam, yielding micrograms of pure clusters within a few hours and the second one uses mass-separated clusters (mass-resolution between 2% and 10%), yielding nanograms of pure clusters in the same timescale. Furthermore, at the second deposition stage, a variety of matrix materials can be co-deposited at a controlled sample temperature between 153 K and 673 K. In order to prove the capabilities of the apparatus, a series of experiments with Fe clusters embedded in Ag matrices with different volume fractions of clusters were carried out. Energy dispersive X-ray spectroscopy measurements revealed that the amount of deposited clusters as well as the sample homogeneity can be controlled with an outstanding accuracy of 10%. Additional measurements of the magnetic properties indicated the presence of separated clusters for volume fractions of clusters around 2 volume percent (vol. %), while above this concentration (10 vol. %) a partial aggregation of the clusters was observed. It was also shown that the resulting thin films are nearly oxygen free, which ascertains that oxygen sensitive materials can be safely handled in this newly developed apparatus.

The mechanically induced structural disorder in barium hexaferrite, BaFe12O19, and its impact on magnetism

The response of the structure of the M-type barium hexaferrite (BaFe₁₂O₁₉) to mechanical action through high-energy milling and its impact on the magnetic behaviour of the ferrite are investigated. Due to the ability of the ⁵⁷Fe Mössbauer spectroscopic technique to probe the environment of the Fe nuclei, a valuable insight on a local atomic scale into the mechanically induced changes in the hexagonal structure of the material is obtained. It is revealed that the milling of BaFe₁₂O₁₉ results in the deformation of its constituent polyhedra (FeO₆ octahedra, FeO₄ tetrahedra and FeO₅ triangular bi-pyramids) as well as in the mechanically triggered transition of the Fe³⁺ cations from the regular 12k octahedral sites into the interstitial positions provided by the magnetoplumbite structure. The response of the hexaferrite to the mechanical treatment is found to be accompanied by the formation of a non-uniform nanostructure consisting of an ordered crystallite surrounded/separated by a structurally disordered surface shell/interface region. The distorted polyhedra and the non-equilibrium cation distribution are found to be confined to the amorphous near-surface layers of the ferrite nanoparticles with the thickness extending up to about 2 nm. The information on the mechanically induced short-range structural disorder in BaFe₁₂O₁₉ is complemented by an investigation of its magnetic behaviour on a macroscopic scale. It is demonstrated that the milled ferrite nanoparticles exhibit a pure superparamagnetism at room temperature. As a consequence of the far-from-equilibrium structural disorder in the surface shell of the nanoparticles, the mechanically treated BaFe₁₂O₁₉ exhibits a reduced magnetization and an enhanced coercivity.

Measurement of the Optic Nerve Sheath Diameter in Children: Comparison Between Transbulbar Sonography and Magnetic Resonance Imaging

PURPOSE

 To evaluate the accuracy of measurements of the optic nerve sheath diameter (ONSD) in children by comparing transbulbar sonography with magnetic resonance imaging (MRI).

MATERIALS AND METHODS

 65 children (age: 3 mo- 17y; mean age: 11.3y) underwent MR imaging of the brain including a heavily T 2-w sequence of the orbit and transbulbar sonography using a 17 MHz linear array transducer. Measurements of the ONSD were performed retrospectively by two experienced readers and all images were evaluated regarding the image quality. Bland-Altman Plots were produced to assess the accuracy of measurements. The correlation between readers and between MR imaging and transbulbar sonography was calculated by the concordance correlation coefficient (CCC).

RESULTS

 Overall the mean values of the ONSD for MRI (5.86 ± 0.66 mm) and transbulbar sonography (5.86 ± 0.71 mm) were identical. There was a high correlation between readers for measurements of the ONSD both for transbulbar sonography (CCC = 0.93) as well as for MRI (CCC = 0.9). Comparing the measurement values between transbulbar sonography and MRI, the correlation of ONSD values was good to moderate with a high dependency on image quality (CCC [0.31, 0.68]).

CONCLUSION

 We were able to demonstrate that the ONSD values of transbulbar sonography in children correlate well with MRI if the relevant anatomic structures are depicted and the measuring points are set correctly. Based on the findings of our study, it seems necessary to define normal and cut-off values for the ONSD in children again to finally assess the clinical relevance of the ONSD as a noninvasive parameter for the evaluation of intracranial pressure.

Fourier transform infrared imaging analysis in discrimination studies of squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) of the oral cavity and oropharynx represents more than 95% of all malignant neoplasms in the oral cavity. Histomorphological evaluation of this cancer type is invasive and remains a time consuming and subjective technique. Therefore, novel approaches for histological recognition are necessary to identify malignancy at an early stage. Fourier transform infrared (FTIR) imaging has become an essential tool for the detection and characterization of the molecular components of biological processes, such as those responsible for the dynamic properties of tumor progression. FTIR imaging is a modern analytical technique enabling molecular imaging of a complex biological sample and is based on the absorption of IR radiation by vibrational transitions in covalent bonds. One major advantage of this technique is the acquisition of local molecular expression profiles, while maintaining the topographic integrity of the tissue and avoiding time-consuming extraction, purification, and separation steps. With this imaging technique, it is possible to obtain unique images of the spatial distribution of proteins, lipids, carbohydrates, cholesterols, nucleic acids, phospholipids, and small molecules with high spatial resolution. Analysis and visualization of FTIR imaging datasets are challenging and the use of chemometric tools is crucial in order to take advantage of the full measurement. Therefore, methodologies for this task based on the novel developed algorithm for multivariate image analysis (MIA) are often necessary. In the present study, FTIR imaging and data analysis methods were combined to optimize the tissue measurement mode after deparaffinization and subsequent data evaluation (univariate analysis and MIAs). We demonstrate that it is possible to collect excellent IR spectra from formalin-fixed paraffin-embedded (FFPE) tissue microarrays (TMAs) of OSCC tissue sections employing an optimised analytical protocol. The correlation of FTIR imaging to the morphological tissue features obtained by histological staining of the sections demonstrated that many histomorphological tissue patterns can be visualized in the colour images. The different algorithms used for MIAs of FTIR imaging data dramatically increased the information content of the IR images from squamous cell tissue sections. These findings indicate that intra-operative and surgical specimens of squamous cell carcinoma tissue can be characterized by FTIR imaging.

Atomic structure and structural stability of Sc75Fe25 nanoglasses

Nanoglasses are solids consisting of nanometer-sized glassy regions connected by interfaces having a reduced density. We studied the structure of Sc(75)Fe(25) nanoglasses by electron microscopy, positron annihilation spectroscopy, and small-/wide-angle X-ray scattering. The positron annihilation spectroscopy measurements showed that the as-prepared nanoglasses consisted of 65 vol% glassy and 35 vol% interfacial regions. By applying temperature annealing to the nanoglasses and measuring in situ small-angle X-ray scattering, we observed that the width of the interfacial regions increased exponentially as a function of the annealing temperature. A quantitative fit to the small-angle X-ray scattering data using a Debye-Bueche random phase model gave a correlation length that is related to the sizes of the interfacial regions in the nanoglass. The correlation length was found to increase exponentially from 1.3 to 1.7 nm when the sample temperature was increased from 25 to 230 °C. Using simple approximations, we correlate this to an increase in the width of interfacial regions from 0.8 to 1.2 nm, while the volume fraction of interfacial regions increased from 31 to 44%. Using micro-compression measurements, we investigated the deformation behavior of ribbon glass and the corresponding nanoglass. While the nanoglass exhibited a remarkable plasticity even in the annealed state owing to the glass-glass interfaces, the corresponding ribbon glass was brittle. As this difference seems not limited to Sc(75)Fe(25) glasses, the reported result suggest that nanoglasses open the way to glasses with high ductility resulting from the nanometer sized microstructure.

High resolution ultrasound and magnetic resonance imaging of the optic nerve and the optic nerve sheath: anatomic correlation and clinical importance

PURPOSE

We performed a cadaver study to evaluate the accuracy of measurements of the optic nerve and the optic nerve sheath for high resolution US (HRUS) and magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Five Thiel-fixated cadaver specimens of the optic nerve were examined with HRUS and MRI. Measurements of the optic nerve and the ONSD were performed before and after the filling of the optic nerve sheath with saline solution. Statistical analysis included the calculation of the agreement of measurements and the evaluation of the intraobserver and interobserver variation.

RESULTS

Overall a good correlation of measurement values between HRUS and MRI can be found (mean difference: 0.02-0.97 mm). The repeatability coefficient (RC) and concordance correlation coefficient (CCC) values were good to excellent for most acquisitions (RC 0.2-1.11 mm; CCC 0.684-0.949). The highest variation of measurement values was found for transbulbar sonography (RC 0.58-1.83 mm; CCC 0.615/0.608).

CONCLUSION

If decisive anatomic structures are clearly depicted and the measuring points are set correctly, there is a good correlation between HRUS and MRI measurements of the optic nerve and the ONSD even on transbulbar sonography. As most of the standard and cut-off values that have been published for ultrasound are significantly lower than the results obtained with MRI, a reevaluation of sonographic ONSD measurement with correlation to MRI is necessary.

Uncommitted precursor cells might contribute to increased incidence of embryonal rhabdomyosarcoma in heterozygous Patched1-mutant mice

Embryonal rhabdomyosarcoma (ERMS) is a tumor of the skeletal muscle in children and is frequently initiated by heterozygous germline mutations in the Hedgehog (Hh) receptor Patched1 (Ptch), both in humans and mice. Using a conditional knock-out strategy in Ptch(flox/+) mice, we demonstrate that early embryonic stages are more susceptible to ERMS development than later stages and that cells normally not committed to undergo myogenesis at this stage represent the major source of ERMS. We found that deletion of a single copy of the Ptch allele at E9.5 using the ubiquitously active Rosa26CreERT2 resulted in a tumor incidence of 88% but reached only 44% and 12% when the Ptch allele was inactivated at E11.5 and E13.5, respectively. Induction of the Ptch mutation at E9.5 did also significantly shorten ERMS-free survival and increased tumor multiplicity compared with tumor induction at E11.5 and E13.5. Interestingly, we observed a more that 10-fold reduction of ERMS incidence when the Ptch mutation was specifically introduced in Myf5-expressing cells, which is the myogenic factor expressed in all muscle cells at E9.5. We conclude that Myf5-negative cells are more susceptible to ERMS development than Myf5-positive embryonic precursors. As the propensity to undergo tumorigenic transformation declined with age, concomitant with the increase of stably committed muscle cells, it seems likely that the Ptch mutation favors tumor formation in progenitor cells, which have not yet acquired a muscle cell fate.

Surface plasmon polariton absorption modulator

An electrically controlled ultra-compact surface plasmon polariton absorption modulator (SPPAM) is proposed. The device can be as small as a few micrometers depending on the required extinction ratio and the acceptable loss. The device allows for operation far beyond 100 Gbit/s, being only limited by RC time constants. The absorption modulator comprises a stack of metal/insulator/metal-oxide/metal layers, which support a strongly confined asymmetric surface plasmon polariton (SPP) in the 1.55 μm telecommunication wavelength window. Absorption modulation is achieved by electrically modulating the free carrier density in the intermediate metal-oxide layer. The concept is supported by proof-of-principle experiments.

Sintering and Deformation of Nanocrystalline Ceramics

Nanocrystalline ceramics have been produced by the method of inert gas condensation of ultra-small particles and in situ consolidation. Sintering characteristics and microstructural parameter such as grain size, porosity and pore size distributions have been investigated by a variety of techniques, including: X-ray diffraction, gravimetry, nitrogen adsorption, scanning electron microscopy and small angle neutron scattering. In pure TiO2, the sintering temperatures are drastically lowered compared to conventional ceramics, however, extensive grain growth occurs before full densification is achieved. High density, nanocrystalline ceramics can be prepared by pressure assisted sintering, doping and additions of second phases. High temperature microhardness and creep deformation in compression were measured and it was found that creep processes occur at lower temperatures than in ceramics with larger grain sizes. Nanocrystalline TiO2 with densities > 99 % can be deformed plastically without fracture at temperatures below half the melting point. The total strains exceed 0.6 at strain rates as high as 10−3 s−1. The stress exponent of the strain rate, n, is approximately 3 and the grain size dependence is G-q with q in the range of 1 – 1.5. It is concluded that the creep deformation occurs by an interface reaction controlled mechanism.

Kinetic and Thermodynamic Properties of Nanocrystalline Materials

A new class of materials with ultra small grain size has recently been synthesized by combining the methods of inert gas condensation of metal vapors and in situ powder compaction. These ‘nanocrystalline’ materials, with grain sizes of 5-10 nm, can have over 30% of their atoms lying in the highly disordered interfaces or grain boundaries. Because of their unique atomic structure, nanocrystalline materials often have properties far different from their bulk counterparts. In addition, kinetic processes can be rapidly accelerated due to the short diffusion distances between grains. In this review, we will report on the thermodynamic properties and reaction kinetics of nanocrystalline metals and on such kinetic properties as sintering and grain growth in nanocrystalline ceramics.

Small Angle Neutron Scattering from Nanophase Titanium As A Function of Oxidation

Nanophase titanium, prepared by the gas-condensation method both as aggregated powder and in lightly compacted discs, has been studied by conventional small angle neutron scattering, and by use of contrast variation methods. The contrast has been changed (a), isotopically, by means of deuterated/protonated solvents distilled into the specimen and (b) by progressive incremental oxidation of the Ti particles using fixed doses of low-pressure oxygen. It was shown that some evolution of the small angle pattern for lightly compacted nanophase Ti occurred over a period of several months at 300 K. Contrast matching by external solvent works well and has allowed the scattering lengths of oxidized and unoxidized specimens to be followed. The results imply that the scattering from metal and oxide can be separated under suitable conditions. The partial oxidation experiments indicate that there is both a fast and slow oxidation at 300 K. Also, during slow oxidation, high scattering length density scattering centers were formed whose number increased, but whose size remained the same at about 2 nm; these centers are tentatively assumed to be TiO2.

Low Temperature Sintering and Deformation of Nanocrystalline TiO2

The sintering and deformation kinetics of nanocrystalline (n-) TiO2 were studied. It was found that pressureless sintering yields densities above 95 % with modest increase in grain size whereas pressure assisted sintering (1GPa) results in high density samples without grain growth. In addition compression tests were performed. Large true strains up to 0.6 and strain rates as high as 8 × 10−5 s−1 were observed at 810 °C without fracturing. The sintering and creep results are discussed in terms of the microstructure and diffusion coefficients in n-TiO2.