Forward flux sampling-type schemes for simulating rare events: efficiency analysis

We analyze the efficiency of several simulation methods which we have recently proposed for calculating rate constants for rare events in stochastic dynamical systems in or out of equilibrium. We derive analytical expressions for the computational cost of using these methods and for the statistical error in the final estimate of the rate constant for a given computational cost. These expressions can be used to determine which method to use for a given problem, to optimize the choice of parameters, and to evaluate the significance of the results obtained. We apply the expressions to the two-dimensional nonequilibrium rare event problem proposed by Maier and Stein [Phys. Rev. E 48, 931 (1993)]. For this problem, our analysis gives accurate quantitative predictions for the computational efficiency of the three methods.     

Exact results for noise power spectra in linear biochemical reaction networks

We present a simple method for determining the exact noise power spectra and related statistical properties for linear chemical reaction networks. The method is applied to reaction networks which are representative of biochemical processes such as gene expression. We find, for example, that a post-translational modification reaction can reduce the noise associated with gene expression. Our results also indicate how to coarse grain networks by the elimination of fast reactions. In this context we have discovered a breakdown of the sum rule which relates the noise power spectrum to the total noise. The breakdown can be quantified by a sum rule deficit, which is found to be universal, and can be attributed to the high-frequency noise in the fast reactions.     

Micromechanical testing of individual collagen fibrils

A novel method based on AFM was used to attach individual collagen fibrils between a glass surface and the AFM tip, to allow force spectroscopy studies of these. The fibrils were deposited on glass substrates that are partly coated with Teflon AF. A modified AFM tip was used to accurately deposit epoxy glue droplets on either end of the collagen fibril that cross the glass-Teflon AF interface, as to such attach it with one end to the glass and the other end to the AFM tip. Single collagen fibrils have been mechanically tested in ambient conditions and were found to behave reversibly up to stresses of 90 MPa. Within this regime a Young's modulus of 2-7 GPa was obtained. In aqueous media, the collagen fibrils could be tested reversibly up to about 15 MPa, revealing Young's moduli ranging from 0.2 to at most 0.8 GPa.     

Short synthesis of functionalized pentalongin derivatives using pyridinium ylid chemistry

3-Substituted pentalongin derivatives possessing an acetal function at C-1 were synthesized by cyclization of acylmethylnaphthoquinones. The latter naphthoquinones were prepared starting from 2-dioxolanylnaphthoquinone by means of both a stoichiometric and a catalytic method deploying various pyridinium ylids.     

ω* has (almost) no continuous images

We prove that the following statement follows from the Open Colouring Axiom (OCA): ifX is locally compactσ-compact but not compact and if its Čech-Stone remainderX* is a continuous image ofω*, thenX is the union ofω and a compact set. It follows that the remainders of familiar spaces like the real line or the sum of countably many Cantor sets need not be continuous images ofω*.     

Highly efficient and safe procedure for the synthesis of aryl 1,2,3-triazoles from aromatic amine in a continuous flow reactor

The Letter reports a safe and reliable synthesis of aryl 1,2,3-triazoles from the corresponding anilines via intermediate aryl azides, using a continuous process. The method was applied to a variety of substrates with good to excellent yields, without the need to isolate the reactive and possibly unstable intermediates which were constantly kept at low concentration in the matrix environment.     

Electroanalytical Study of the Pesticide Asulam

The electrochemical behaviour of the herbicide Asulam was studied by cyclic and square wave voltammetry. Asulam may be irreversibly oxidised at a glassy carbon electrode. Maximum currents were obtained at pH = 1.9 in aqueous electrolyte solution. Based on the electrochemical behaviour of Asulam, two analytical methodologies were developed for its determination in water samples, using square wave voltammetry (SWV) and flow injection analysis (FIA) coupled with an amperometric detector. Limits of detection of 7.1 2 10 m 6 mol L m 1 and 1.2 2 10 m 8 mol L m 1 for SWV and FIA respectively, were achieved. Repeatability was calculated by assessing the relative standard deviation (%) for 10 consecutive determinations of one sample. The found values were 2.1% for SWV and 5.0% for FIA. Validation of the results provided by SWV and FIA methodologies was performed by comparison with results from an HPLC-DAD technique. Good relative deviations were found (< 5%). Recovery trials were performed to assess the accuracy of the results and the obtained values were between 84% and 107% for both methods.     

Moments of the Mean of Dubins–Freedman Random Probability Distributions

Explicit formulas are given to recursively generate the moments of the mean M for Dubins–Freedman random distribution functions with arbitrary base measure . Using a standard inversion formula for moments of a distribution on the unit interval, the distribution of M is approximated for several natural choices of . The support of the mean is also considered. It is shown that the support of M is connected whenever is concentrated on the vertical bisector of the unit square S, but may have arbitrarily many gaps otherwise.     

Formation of the chromophore of the pyoverdine siderophores by an oxidative cascade

The pyoverdine chromophore is formed in a reaction involving a two-electron oxidation, a conjugate addition, and a second two-electron oxidation. This oxidative cascade can be carried out with polyphenol oxidase (PPO), MnO(2), and cell-free extracts from Pseudomonas aeruginosa. [reaction: see text]