Nonlinear effect of tooth-slot transition on axial vibration, contact state and speed fluctuation in traveling wave ultrasonic motor

The tooth-slot transition creates an axial excitation on traveling wave ultrasonic motors. It induces a rotor’s axial rigid vibration, which in turn affects the contact state and arouses speed fluctuation. To gain an insight into this problem, this work examines the relationships between the tooth-slot transition, axial vibration, nonlinear contact, and speed fluctuation. An analytical model governing rotor’s vibration is developed, where the transition force, nonlinear contact stiffness, and pre-pressure are included. The contact stiffness is demonstrated to decrease with an increase in stator’s vibration amplitude and it is approximated by polynomial fitting such that the nonlinear problem can be analytically solved. The primary, 1/2 subharmonic, and 2/1 superharmonic resonances are analyzed to determine the amplitude–frequency response and steady-state response. Nonlinear phenomena regarding the three types of resonances are identified. The interaction between the transition force, axial vibration, contact stiffness and speed fluctuation is investigated through a new contact model. The results imply that the rotor vibration induces rotating acceleration and leads to speed fluctuation. In addition, the rotor speed fluctuates in a similar fashion with the axial vibration.

A stretched conformation of DNA with a biological role?

We have discovered a well-defined extended conformation of double-stranded DNA, which we call Σ-DNA, using laser-tweezers force-spectroscopy experiments. At a transition force corresponding to free energy change ΔG = 1·57 ± 0·12 kcal (mol base pair)−1 60 or 122 base-pair long synthetic GC-rich sequences, when pulled by the 3′−3′ strands, undergo a sharp transition to the 1·52 ± 0·04 times longer Σ-DNA. Intriguingly, the same degree of extension is also found in DNA complexes with recombinase proteins, such as bacterial RecA and eukaryotic Rad51. Despite vital importance to all biological organisms for survival, genome maintenance and evolution, the recombination reaction is not yet understood at atomic level. We here propose that the structural distortion represented by Σ-DNA, which is thus physically inherent to the nucleic acid, is related to how recombination proteins mediate recognition of sequence homology and execute strand exchange. Our hypothesis is that a homogeneously stretched DNA undergoes a ‘disproportionation’ into an inhomogeneous Σ-form consisting of triplets of locally B-like perpendicularly stacked bases. This structure may ensure improved fidelity of base-pair recognition and promote rejection in case of mismatch during homologous recombination reaction. Because a triplet is the length of a gene codon, we speculate that the structural physics of nucleic acids may have biased the evolution of recombinase proteins to exploit triplet base stacks and also the genetic code.

Usability Study of Self-Service System in Gadjah Mada University Library

Changing system from conventional to self-service system brings many advantages for a better service. In other hand, this transition force people to adapt with the new system.This research aimed to identify usability of self-service system in library, particularly in the Standard Operating Procedure (SOP) on loans process. The methods of this research consist of user tasking, questionnaires, and open ended interviews. Usability testing conducted based on usability attributes including effectiveness, efficiency, and satisfaction. After obtaining the test result from the data, the statistical tests related data attributes are analyzed using independent t-test. The results of this study showed a significant difference between the initial conditions and the improved condition. The improved loans procedures give better result than the existing one.

Experimental and Numerical Studies on B-DNA Overstretching Transition in Presence of Sodium Ions at Physiological Temperature

In this paper, the effects of Na+ concentration on the overstretching transition of B-DNA molecule at physiological temperature are studied by both experimental and numerical methods. Using optical tweezers, the relationship of external force and relative extension is obtained by stretching single B-DNA molecule at 37°C. As the concentration increases from 0.909mM to 909mM, the overstretching transition force increases from 65.65 ± 1.2pN to 43.07 ± 1.2pN. An analytical expression is derived, which shows that overstretching transition force is linear with the natural logarithm of salt concentration. Based on a previous model, a three-dimensional model is proposed herein and solved by Metropolis Monte Carlo method. The bending deformation of DNA backbones, cooperativity of base-stacking interactions, electrostatic interactions, and spatial effects of DNA double helix structure are taken into account. Our key contribution is that the electrostatic energy is explicitly given as a function of folding angle and Na+ concentration. A new parameter is also introduced to account for the cooperativity of base-stacking interactions. The numerical results of this model are in good agreement with our experimental results.