Quantile process for left truncated and right censored data

In this paper, we consider the product-limit quantile estimator of an unknown quantile function when the data are subject to random left truncation and right censorship. This is a parallel problem to the estimation of the unknown distribution function by the product-limit estimator under the same model. Simultaneous strong Gaussian approximations of the product-limit process and product-limit quantile process are constructed with rate . A functional law of the iterated logarithm for the maximal deviation of the estimator from the estimand is derived from the construction. Work partially supported by NSC Grant 89-2118-M-259-011.     

Chemical bonding, electron-phonon coupling, and structural transformations in high-pressure phases of Si

The nature of chemical bonding of the stable phases of Si at high pressure was analyzed. The effect of pressure is to promote sp electrons into the d orbitals, thus increasing the metallic character and reducing the dimensionality of covalent bonding. Localized covalent bonds, however, persist up to approximately 40 GPa (Si-VI, Cmca) and help to stabilize directional framework structures. At high pressures, Si becomes a metal, and the usual dense packed structures prevail. The existence of conducting and localized electrons gives rise to a combination of "steep and flat bands" near the Fermi level in Si-V. This peculiar electron topology in conjunction with low-frequency vibrations contributes to the relatively high superconducting temperature in Si-V and VI.     

New synthetic protocols for the preparation of unsymmetrical bisindoles

Novel unsymmetrical bisindoles were synthesized by a solvent-free C-C bond-formation reaction under mild conditions. Starting from aziridines or hydroxyl precursors, indoles have been used as C-nucleophiles to form new pharmacologically interesting bisindoles via an electrophilic aromatic substitution pathway in good to excellent yields. [reaction: see text]     

Valence band x-ray emission spectra of compressed germanium

We report measurements of the valence band width in compressed Ge determined from x-ray emission spectra below the Ge K edge. The width of the valence band does not show any pressure dependence in the semiconducting diamond-type structure of Ge below 10 GPa. On the other hand, in the metallic beta-Sn phase above 10 GPa the valence band width increases under compression. Density-functional calculations show an increasing valence band width under compression both in the semiconducting phase (contrary to experiment) and in the metallic beta-Sn phase of Ge (in agreement with observed pressure-induced broadening). The pressure-independent valence band width in the semiconducting phase of Ge appears to require theoretical advances beyond the density-functional theory or the GW approximation.     

Comparison Between the Mean-Variance Optimal and the Mean-Quadratic-Variation Optimal Trading Strategies

ABSTRACT

We compare optimal liquidation policies in continuous time in the presence of trading impact using numerical solutions of Hamilton–Jacobi–Bellman (HJB) partial differential equations (PDEs). In particular, we compare the time-consistent mean-quadratic-variation strategy with the time-inconsistent (pre-commitment) mean-variance strategy. We show that the two different risk measures lead to very different strategies and liquidation profiles. In terms of the optimal trading velocities, the mean-quadratic-variation strategy is much less sensitive to changes in asset price and varies more smoothly. In terms of the liquidation profiles, the mean-variance strategy is much more variable, although the mean liquidation profiles for the two strategies are surprisingly similar. On a numerical note, we show that using an interpolation scheme along a parametric curve in conjunction with the semi-Lagrangian method results in significantly better accuracy than standard axis-aligned linear interpolation. We also demonstrate how a scaled computational grid can improve solution accuracy.     

Chirality-induced dynamic kohn anomalies in graphene

We develop a theory for the renormalization of the phonon energy dispersion in graphene due to the combined effects of both Coulomb and electron-phonon (e-ph) interactions. We obtain the renormalized phonon energy spectrum by an exact analytic derivation of the phonon self-energy, finding three distinct Kohn anomalies (KAs) at the phonon wave vector q=omega/v, 2k_{F}+/-omega/v for LO phonons and one at q=omega/v for TO phonons. The presence of these new KAs in graphene, in contrast to the usual KA q=2k_{F} in ordinary metals, originates from the dynamical screening of e-ph interaction (with a concomitant breakdown of the Born-Oppenheimer approximation) and the peculiar chirality of the graphene e-ph coupling.     

Monochalcoplatin: An Actively Transported,Quickly Reducible,and Highly Potent PtIV Anticancer Prodrug

Recently, Pt^IV prodrugs have attracted much attention as the next generation of platinum‐based antineoplastic drug candidates. Here we report the discovery and evaluation of monochalcoplatin, a monocarboxylated Pt^IV prodrug that is among the most cytotoxic Pt^IV prodrugs to date. Compared with its dicarboxylated counterpart chalcoplatin, monochalcoplatin accumulates astonishingly effectively and rapidly in cancer cells, which is not ascribed to its lipophilicity. The prodrug is quickly reduced, causes DNA damage, and induces apoptosis, resulting in superior cytotoxicity with IC₅₀ values in the nanomolar range in both cisplatin‐sensitive and ‐resistant cells; these IC₅₀ values are up to 422‐fold higher than that of cisplatin. A detailed mechanistic study reveals that monochalcoplatin actively enters cells through a transporter‐mediated process. Moreover, monochalcoplatin shows significant antitumor activity in an in vivo colorectal tumor model. Our study implies a practical strategy for the design of more effective Pt^IV prodrugs to conquer drug resistance by tuning both cellular uptake pathways and activation processes.     

Controlling Proton and Electron Transfer Rates to Enhance the Activity of an Oxygen Reduction Electrocatalyst

An electrochemical approach is developed that allows for the control of both proton and electron transfer rates in the O₂ reduction reaction (ORR). A dinuclear Cu ORR catalyst was prepared that can be covalently attached to thiol‐based self‐assembled monolayers (SAMs) on Au electrodes using azide–alkyne click chemistry. Using this architecture, the electron transfer rate to the catalyst is modulated by changing the length of the SAM, and the proton transfer rate to the catalyst is controlled with an appended lipid membrane modified with proton carriers. By tuning the relative rates of proton and electron transfer, the current density of the lipid‐covered catalyst is enhanced without altering its core molecular structure. This electrochemical platform will help identify optimal thermodynamic and kinetic parameters for ORR catalysts and catalysts of other reactions that involve the transfer of both protons and electrons.     

Development and characterization of bottom-viewed inductively coupled plasma-atomic emission spectrometry

In bottom-viewed inductively coupled plasma-atomic emission spectrometry (BV-ICP-AES), emission from the central channel of the plasma is measured axially from the bottom of the plasma. A straight quartz tube was used as a hollow light pipe (HLP) to collect plasma emission in this study. The HLP also serves as an injector for aerosols transport and injection into the ICP. The optical characteristics of HLPs with the original reflective surface and roughened outer surface are reported. The roughened HLP is effective in rejecting light beams that are not in line with the HLP. The transmission efficiency of the HLP, however, is high (> 70%) for light beams from a source that has the same dimension as the entrance of the HLP and is flush with the HLP. The HLP is effective in rejecting background emission from the core of the plasma that encircles the plasma central channel and yet efficient in light collection from the central channel of the plasma.     

Front Cover: Synthesis,Characterization, and Cytotoxicity of a Reactive Platinum(IV) Monotrifluoromethyl Complex (Eur. J. Inorg. Chem. 3/2023)

Platinum-based complexes are among the most widely utilized cancer therapeutics. Current Pt(II) drugs face some challenges including toxicity and drug resistance. To solve these issues, great efforts have been devoted to developing nonclassical platinum complexes, such as Pt(IV) prodrugs, that act via mechanisms distinct from those of the approved drugs. Compared with active Pt(II) counterparts, Pt(IV) complexes are relatively inert. Although direct interactions between Pt(IV) complexes and nucleotides have been reported, the reaction is slow due to the kinetic inertness of Pt(IV) complexes. Herein, we design and synthesize a Pt(IV) monotrifluoromethyl complex, in which the chloride ligand that is trans to trifluoromethyl ligand is reactive. The Pt(IV) monotrifluoromethyl complex is very stable in water but displays high reactivity towards various substrates including buffer components and 5’-dGMP. The study of reaction mechanism reveals that this Pt(IV) complex reacts with phosphate via S_N2 nucleophilic substitution pathway, which is different from Pt(II) drugs. The Pt(IV) monotrifluoromethyl complex is cytotoxic in human ovarian cancer cells. Our work reports an example of a reactive organometallic Pt(IV) complex that can directly interact with nucleophiles and implies its potential as an anticancer agent.