A distributed dynamic mesh model of a helical gear pair with tooth profile errors

A dynamic model of a helical gear rotor system is proposed.Firstly,a generally distributed dynamic model of a helical gear pair with tooth profile errors is developed.The gear mesh is represented by a pair of cylinders connected by a series of springs and the stiffness of each spring is equal to the effective mesh stiffness.Combining the gear dynamic model with the rotor-bearing system model,the gear-rotor-bearing dynamic model is developed.Then three cases are presented to analyze the dynamic responses of gear systems.The results reveal that the gear dynamic model is effective and advanced for general gear systems,narrow-faced gear,wide-faced gear and gear with tooth profile errors.Finally,the responses of an example helical gear system are also studied to demonstrate the influence of the lead crown reliefs and misalignments.The results show that both of the lead crown relief and misalignment soften the gear mesh stiffness and the responses of the gear system increase with the increasing lead crown reliefs and misalignments.

Parallel DNA Constrained by“CC^+Clamps”

Parallel DNA helices with reverse WatsonCrick pairing have been described in several papers.It has been pointed out,however,that the parallel structures may also be in equilibrium with antiparallel WatsonCrick helices due to their closely similar properties.To avoid the problem we have prepared and characterized DNA helices which are constrained to possess parallel polarity by two dC residues,or CC+clamps,at both the ends of AT oligomer chains.The residues are hemiprotonated below neutral pH,forming two stable CC+base pairs with three hydrogen bonds at each end of the helix.The physical properties of these constructs can then be used to calibrate those of duplexes having the same sequences but lacking the terminal C residues.Though recent studies indicate that dC acid selfstructures are fourstranded with intercalated bases,gel electrophoresis indicates that these structures are not present in the molecules described here.

Recent studies of atomic-resolution structures of tau protein and structure-based inhibitors

Background:Alzheimer’s disease(AD)is one of the most popular tauopathies.Neurofibrillary tangles and senile plaques are-widely recognized as the pathological hallmarks of AD,which are mainly composed of tau andβ-amyloid(Aβ)respectively.Recent failures of drugs targeting Aβhave led scientists to scrutinize the crucial impact of tau in neurodegenerative diseases.Mutated or abnormal phosphorylated tau protein loses affinity with microtubules and assembles into pathological accumulations.The aggregation process closely correlates to two amyloidogenic core of PHF6(^(306)VQIVYK^(311))and PHF6*(^(275)VQILNK^(280))fragments.Moreover,tau accumulations display diverse morphological characteristics in different diseases,which increases the difficulty of providing a unifying neuropathological criterion for early diagnosis.Results:This review mainly summarizes atomic-resolution structures of tau protein in the monomeric,oligomeric and fibrillar states,as well as the promising inhibitors designed to prevent tau aggregation or disaggregate tau accumulations,recently revealed by experimental and computational studies.We also systematically sort tau functions,their relationship with tau structures and the potential pathological processes of tau protein.Conclusion:The current progress on tau structures at atomic level of detail expands our understanding of tau aggregation and related pathology.We discuss the difficulties in determining the source of neurotoxicity and screening effective inhibitors.We hope this review will inspire new clues for designing medicines against tau aggregation and shed light on AD diagnosis and therapies.