Threshold photoelectron photoion coincidence spectroscopy and selected ion flow tube reactions of CHF3: comparison of product branching ratios

The threshold photoelectron and threshold photoelectron photoion coincidence spectra of CHF$_3$ in the range 13.5 – 24.5 eV have been recorded. Ion yields and branching ratios have been determined for the three fragments CF$_3^+$, CHF2$^+$ and CF$^+$. The mean kinetic energy releases into fragment ions involving either C-H or C-F bond cleavage have been measured, and compared with statistical and impulsive models. CHF$_3^+$ behaves in a non-statistical manner characteristic of the small-molecule limit, with the ground electronic state and low-lying excited states of CHF$_3^+$ being largely repulsive along the C-H and C-F coordinates, respectively. The rate coefficients and product ion branching ratios have been measured at 298 K in a selected ion flow tube for the reactions of CHF$_3$ with a large number of gas-phase cations whose recombination energies span the range 6.3 through 21.6 eV. A comparison between the branching ratios from the two experiments, together with an analysis of the threshold photoelectron spectrum of CHF$_3$, shows that long-range charge transfer probably occurs for the Ar$^+$ and F$^+$ atomic ions whose recombination energies lie above ca. 15 eV. Below this energy, the mechanism involves a combination of short-range charge transfer and chemical reactions involving a transition state intermediate

Non-Transferable Proxy Re-Encryption Scheme

SEC8: Selected topics in Information SecurityA proxy re-encryption (PRE) scheme allows a proxy to re-encrypt a ciphertext for Alice (delegator) to a ciphertext for Bob (delegatee) without seeing the underlying plaintext. However, existing PRE schemes generally suffer from at least one of the followings. Some schemes fail to provide the non-transferable property in which the proxy and the delegatee can collude to further delegate the decryption right to anyone. This is the main open problem left for PRE schemes. Other schemes assume the existence of a fully trusted private key generator (PKG) to generate the re-encryption key to be used by the proxy for re-encrypting a given ciphertext for a target delegatee. But this poses two problems in PRE schemes if the PKG is malicious: the PKG in their schemes may decrypt both original ciphertexts and re-encrypted ciphertexts (referred as the key escrow problem); and the PKG can generate reencryption key for arbitrary delegatees without permission from the delegator (we refer to it as the PKG despotism problem). In this paper, we propose the first non-transferable proxy re-encryption scheme which successfully achieves the nontransferable property. We show that the new scheme solved the PKG despotism problem and key escrow problem as well. © 2012 IEEE.published_or_final_versio

Epigenetic Inactivation of the miR-124-1 in Haematological Malignancies

miR-124-1 is a tumour suppressor microRNA (miR). Epigenetic deregulation of miRs is implicated in carcinogenesis. Promoter DNA methylation and histone modification of miR-124-1 was studied in 5 normal marrow controls, 4 lymphoma, 8 multiple myeloma (MM) cell lines, 230 diagnostic primary samples of acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), MM, and non-Hodgkin's lymphoma (NHL), and 53 MM samples at stable disease or relapse. Promoter of miR-124-1 was unmethylated in normal controls but homozygously methylated in 4 of 4 lymphoma and 4 of 8 myeloma cell lines. Treatment of 5-Aza-2′-deoxycytidine led to miR-124-1 demethylation and re-expression of mature miR-124, which also associated with emergence of euchromatic trimethyl H3K4 and consequent downregulation of CDK6 in myeloma cells harboring homozygous miR-124-1 methylation. In primary samples at diagnosis, miR-124-1 methylation was absent in CML but detected in 2% each of MM at diagnosis and relapse/progression, 5% ALL, 15% AML, 14% CLL and 58.1% of NHL (p<0.001). Amongst lymphoid malignancies, miR-124-1 was preferentially methylated in NHL than MM, CLL or ALL. In primary lymphoma samples, miR-124-1 was preferentially hypermethylated in B- or NK/T-cell lymphomas and associated with reduced miR-124 expression. In conclusion, miR-124-1 was hypermethylated in a tumour-specific manner, with a heterochromatic histone configuration. Hypomethylation led to partial restoration of euchromatic histone code and miR re-expression. Infrequent miR-124-1 methylation detected in diagnostic and relapse MM samples showed an unimportant role in MM pathogenesis, despite frequent methylation found in cell lines. Amongst haematological cancers, miR-124-1 was more frequently hypermethylated in NHL, and hence warrants further study

Highly ordered CdS nanoparticle arrays on silicon substrates and photoluminescence properties

Highly ordered cadmium sulphide (CdS) nanoparticle (NP) arrays were fabricated on silicon (Si) substrates using ultrathin alumina membranes as evaporation masks. The CdS NPs are polycrystalline and are composed of ultrasmall closely packed nanocrystallites. These crystallites increase in size as the duration of the CdS evaporation process increases. When the thickness of the NPs changes from about 10 to 50 nm, the size of the crystallites increases from about 5–14 to 20–40 nm. Photoluminescence measurements on the CdS NP arrays show a strong emission spectrum with two subbands that are attributed to band-edge and surface-defect emissions. The peak position and width of the band-edge emission band are closely related to the size of the crystallites in the CdS NPs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87842/2/103106_1.pd

Dopant Profile Extraction by Inverse Modeling of Scanning Capacitance Microscopy Using Peak dC/dV

Scanning capacitance microscopy (SCM) has proven to be successful for junction delineation. However quantitative dopant profile extraction by SCM still remains a difficult challenge, due to limited understanding of relevant physics especially at p-n junction, as well as difficulties to accurately quantify all parameters in modeling. In this paper we present a new procedure, the use of peak dC/dV at every spatial point, for dopant profile extraction. The advantage of such a technique is twofold. First it eliminates problems encountered using a fixed dc bias such as contrast reversal. Second, it also excludes the need to model interface traps. This is because the peak dC/dV value is independent of the presence of interface traps, as demonstrated in our experimental results. Furthermore, based on our understanding of the influence of mobility degradation at p-n junction, we propose that low surface mobility model should be used in simulation so that only the accumulation-to-depletion dC/dV is extracted

Atypical burkitt's lymphoma transforming from follicular lymphoma

Amongst follicular lymphoma that transforms into a high-grade lymphoma, majority are diffuse large B cell lymphoma. Here we reported a rare atypical Burkitt's lymphoma transformation from an asymptomatic follicular lymphoma. Lymph node biopsy showed a composite lymphoma with infiltration of the inter-follicular areas by high grade small non-cleaved lymphoma cells amongst neoplastic follicles. Moreover, FISH and molecular genetic study confirmed concomitant MYC translocations and t(14;18) in the high-grade component, thereby suggesting the transformation of atypical Burkitt's lymphoma from an undiagnosed antecedent follicular lymphoma. The disease followed an aggressive clinical course, terminating in refractory disease 13 months after diagnosis. This is followed by a comprehensive review of the literature on lymphoma transformations from underlying follicular lymphoma after acquisition of MYC translocation, using Burkitt's lymphoma, follicular lymphoma, transformation and MYC translocations as keywords

Monitoring oxide quality using the spread of the dC/dV peak in scanning capacitance microscopy measurements

This article proposes a method for evaluating the quality of the overlying oxide on samples used in scanning capacitance microscopy (SCM) dopant profile extraction. The method can also be used generally as a convenient in-process method for monitoring oxide quality directly after the oxidation process without prior metallization of the oxide-semiconductor sample. The spread of the differential capacitance characteristic (dC/dV versus V plot), characterized using its full width at half maximum (FWHM), was found to be strongly dependent on the interface trap density as a consequence of the stretch-out effect of interface traps on the capacitance-voltage (C-V) curve. Results show that the FWHM of the dC/dV characteristic is a sensitive monitor of oxide quality (in terms of interface trap density) as it is not complicated by localized oxide charging effects as in the case of the SCM probe tip voltage corresponding to maximum dC/dV. The magnitude of the dC/dV peak, at any given surface potential, was also found to be independent of the interface traps and only dependent on the substrate dopant concentration, which makes SCM dopant profile extraction possible

Fabrication of Highly Ordered Nanoparticle Arrays Using Thin Porous Alumina Masks

Highly ordered nanoparticle arrays have been successfully fabricated by our group recently using ultra-thin porous alumina membranes as masks in the evaporation process. The sizes of the nanoparticles can be adjusted from 5-10 nm to 200 nm while the spacing between adjacent particles can also be adjusted from several nanometers to about twice the size of a nanoparticle. The configuration of the nanoparticles can be adjusted by changing the height of the alumina masks and the evaporation direction. Due to the high pore regularity and good controllability of the particle size and spacing, this method is useful for the ordered growth of nanocrystals. Different kinds of nanoparticle arrays have been prepared on silicon wafer including semiconductors (e.g., germanium) and metals (e.g., nickel). The germanium nanoparticle arrays have potential applications in memory devices while the nickel catalyst nanoparticle arrays can be used for the growth of ordered carbon nanotubes.Singapore-MIT Alliance (SMA