An amphiphilic polymer for the synthesis of diverse polymer libraries exemplified using conjugates with lower critical solution temperatures that span water's liquid state

The discovery of new polymer functions is intrinsically tied to the synthesis of diverse structures. Herein we report the synthesis of a new polymer library precursor, poly[N-(12-carboxyl-3,6,9-trioxado) methacrylamide] (pCTMAAm), that is functionalizable with hydrophilic or hydrophobic ligands in both protic and aprotic solvents. The polymer is made through RAFT polymerization with narrow dispersities. Carboxylic acid groups terminate the pCTMAAm side chains, which allows conjugation of both hydrophobic and hydrophilic groups. As a demonstration, three very different ligands, agmantine (cation), galactosamine (polyol) and hexylamine (hydrophobic), were conjugated to pCTMAAm using DMTTM as a condensing agent with greater than 80% conjugation efficiency. To demonstrate the potential utility of the amphiphilic polymer, a polymer library containing side chains with a series of alkanes and varying degrees of substitution was synthesized showing lower critical solution temperature (LCST) profiles that span a temperature range of 7 °C to above 90 °C in water. Multivariate linear regression analysis of the polymer library was used to understand how polymer composition correlates to LCST, using molecular weight, alkane length and degree of substitution as continuous variables. The outcome showed that alkane length has the greatest influence on LCST and that LCST can be estimated using these material composition inputs.     

Pulse synthesis in the single-cycle regime from independent mode-locked lasers using attosecond-precision feedback

We report the synthesis of a nearly single-cycle (3.7?fs), ultrafast optical pulse train at 78?MHz from the coherent combination of a passively mode-locked Ti:sapphire laser (6?fs pulses) and a fiber supercontinuum (1-1.4?μm, with 8?fs pulses). The coherent combination is achieved via orthogonal, attosecond-precision synchronization of both pulse envelope timing and carrier envelope phase using balanced optical cross-correlation and balanced homodyne detection, respectively. The resulting pulse envelope, which is only 1.1 optical cycles in duration, is retrieved with two-dimensional spectral shearing interferometry (2DSI). To our knowledge, this work represents the first stable synthesis of few-cycle pulses from independent laser sources.     

Ultra-incompressible Ternary Diborides Re_（0.5）Ir_（0.5）B_2,Re_（0.5）Tc_（0.5）B_2,Os_（0.5）W_（0.5）B_2 and Os_（0.5）Ru_（0.5）B_2：Density Functional Calculation

In this paper, density functional computations have been applied to the structural, elastic and electronic properties of ternary transition metal diborides Re0.5Ir0.5B2, Re0.5Tc0.5B2, Os0.5W0.5B2 and Os0.5Ru0.5B2 in hexagonal (P63/mmc) and orthorhombic (Pmmn) structures with both local density approximation and generalized gradient approximation. LDA gives smaller lattice parameters and larger elastic moduli than GGA. Both results show that the hexagonal ones are more stable than orthorhombic ones except Os0.5Ru0.5B2. Moreover, the hexagonal structure has superior elastic property than orthorhombic one. Generally speaking, the calculated elastic moduli of Re0.5Ir0.5B2 and Os0.5Ru0.5B2 are smaller than those values of Re0.5Tc0.5B2 and Os0.5W0.5B2 within the same structure because of the filling of antibonding states. The relativistic effects result in weaker bonds of Tc-B (Ru-B) than those of Re-B (Os-B). All the diborides are ultra-incompressible. Re0.5Tc0.5B2 has the largest shear modulus and it is a promising superhard diboride like Os0.5W0.5B2. The elastic properties are in high correlation with the bond strength. The shear moduli are more sensitive than the bulk moduli to the bond strength.     

On the mechanism of unsteady shock oscillation in shock wave/turbulent boundary layer interactions

An experimental investigation into the mechanism of shock wave oscillation in compression ramp-generated shock wave/turbulent boundary layer interactions is presented. Particular emphasis is focused upon documenting the respective roles played by both burst-sweep events in the turbulent boundary layer immediately upstream of the interaction and the downstream separated shear layer upon unsteady shock front motion. Unlike the majority of compression ramp experiments which involve bulk separation and large-scale shock motion, consideration is given here to comparatively “weak” interactions in which the streamwise spatial excursion of the shock front is always less than one boundary layer thickness. In this manner any shock motion due to upstream burst-sweep events should be more apparent in relation to that oscillation associated with the separated region. A discrete Hilbert transform-based conditional sampling technique is used to obtain wall pressure measurements conditioned to burst-sweep events. The conditional sampling technique forms the basis by which the instantaneous shock motion is conditioned to the occurrence of upstream bursting. The relationship between the separation bubble and shock motion is also explored in detail. The results of the experiments indicate that the separation bubble represents a first-order effect on shock oscillation. Although it is demonstrated theoretically that the burst-sweep cycle can also give rise to unsteady shock motion of much lower amplitude, the experiments clearly demonstrate that there is no discernible statistical relationship between burst events and spanwise coherent shock front motion.     

催化光度法测定痕量钒——钒(Ⅴ)-溴甲酚紫-过氧化氢体系

催化光度法测定钒已有报道[1～3],在0.45 mol·L-1磷酸介质及加热条件下,过氧化氢氧化溴甲酚紫褪色反应非常缓慢,而痕量钒对此反应具有较高的催化活性,且在一定浓度范围内,钒量与褪色反应程度呈线性关系,据此可建立测定痕量钒的方法.方法的检出限为1.9×10-6g·L-1,测定范围为0.003～1.8 mg·L-1.方法操作简便,重现性好,用于钢样中痕量钒的测定,结果满意.     

Der Nachweis von Gold in Mineralien

Ohne Zusammenfassung     

The Ordered K-Theory of C/*-Algebras¶Associated with Substitution Tilings

We consider the C ^*-algebra, A _T , constructed from a substitution tiling system which is primitive, aperiodic and satisfies the finite pattern condition. Such a C ^*-algebra has a unique trace. We show that this trace completely determines the order structure on the group K ₀(A _T ); a non-zero element in K ₀(A _T ) is positive if and only if its image under the map induced from the trace is positive. Received: 12 August 1999 / Accepted: 2 May 2000     

Characterizing the Memory Effect on the amylose tris(3,5-dimethylphenyl) carbamate stationary phase

Acid/base modifiers are sometimes used as additives in normal phase elution on columns packed with CHIRALPAK^® AD^®. They affect enantioseparations in ways that are not understood for the lack of systematic studies, which makes the scale-up of preparative separations difficult to predict. Once a column has been exposed to these modifiers, the selectivity of certain pairs of enantiomers may change, for the better or the worse. Numerous molecules that are affected by this phenomenon are listed in the literature. We selected five of them, the selectivity of which changes as more acidic or basic solutions are percolated through the column. The selectivity of ketoprofen, 4-chlorophenylalanine methyl and ethyl esters improves as a solution of Ethanesulfonic Acid is percolated through the column. The selectivity of Propranolol HCl and Tröger’s base increases as a solution of diisopropylamine is percolated through the column. Each one of these five compounds is inversely affected by the percolation of the opposite acid/base solution. We used trans-Stilbene Oxide (tso) as a “standard” to determine the columns stability because no Memory Effect is observed for it (its retention, enantioselectivity, and resolution remain constant). Karl Fisher titrations showed that only slight changes in the water content of the mobile phase occurred, and that a unique water to polymer moiety ratio is important. Analytical studies of the stationary phase suggest that slow protonation/deprotonation of water attached to the carbamate moiety may be responsible for the acid/base Memory Effect. Finally, we showed that the Memory Effect can be minimized by percolating through the column a sufficiently concentrated solution of the appropriate acid or base. Thus, columns that were unreliable for method development, due to the Memory Effect, can now be used. As a result, the need to store several CHIRALPAK AD columns, specific for each condition of the Memory Effect, is eliminated.