Energetics of cytoskeletal gel contraction.

Cytoskeletal gels are prototyped to reproduce the mechanical contraction of the cytoskeleton in vitro. They are composed of a polymer network (backbone), swollen by the presence of a liquid solvent, and active molecules (molecular motors, MMs) that transduce chemical energy into the mechanical work of contraction. These motors attach to the polymer chains to shorten them and/or act as dynamic crosslinks, thereby constraining the thermal fluctuations of the chains. We describe both mechanisms thermodynamically as a microstructural reconfiguration, where the backbone stiffens to motivate solvent (out)flow and accommodate contraction. Via simple steady-state energetic analysis, under the simplest case of isotropic deformation, we quantify the mechanical energy required to achieve contraction as a function of polymer chain density and molecular motor density. We identify two limit regimes, namely, fast MM activation (FM), and slow MM activation (SM). FM assumes that MMs provide all the available mechanical energy 'instantaneously' and leave the polymer in a stiffened state, i.e. the MM activity occurs at a time scale that is much smaller than that of solvent diffusion. SM assumes that the timescale for MM activation is much longer than that of solvent diffusion. To achieve the same final contracted state, FM requires the largest amount of work per unit reference volume, while SM requires the least. For all intermediate cases where the timescale of MM activation is comparable with that of solvent diffusion, the required work ranges between these two limits. We provide all these quantities as a function of chain density and MM density. Finally, we compare our results on contraction energetics with experiments and observe good agreement.

Candidate Tidal Disruption Event AT2019fdr Coincident with a High-Energy Neutrino.

The origins of the high-energy cosmic neutrino flux remain largely unknown. Recently, one high-energy neutrino was associated with a tidal disruption event (TDE). Here we present AT2019fdr, an exceptionally luminous TDE candidate, coincident with another high-energy neutrino. Our observations, including a bright dust echo and soft late-time x-ray emission, further support a TDE origin of this flare. The probability of finding two such bright events by chance is just 0.034%. We evaluate several models for neutrino production and show that AT2019fdr is capable of producing the observed high-energy neutrino, reinforcing the case for TDEs as neutrino sources.

A 62-minute orbital period black widow binary in a wide hierarchical triple.

Over a dozen millisecond pulsars are ablating low-mass companions in close binary systems. In the original 'black widow', the eight-hour orbital period eclipsing pulsar PSR J1959+2048 (PSR B1957+20)1, high-energy emission originating from the pulsar2 is irradiating and may eventually destroy3 a low-mass companion. These systems are not only physical laboratories that reveal the interesting results of exposing a close companion star to the relativistic energy output of a pulsar, but are also believed to harbour some of the most massive neutron stars4, allowing for robust tests of the neutron star equation of state. Here we report observations of ZTF J1406+1222, a wide hierarchical triple hosting a 62-minute orbital period black widow candidate, the optical flux of which varies by a factor of more than ten. ZTF J1406+1222 pushes the boundaries of evolutionary models5, falling below the 80-minute minimum orbital period of hydrogen-rich systems. The wide tertiary companion is a rare low-metallicity cool subdwarf star, and the system has a Galactic halo orbit consistent with passing near the Galactic Centre, making it a probe of formation channels, neutron star kick physics6 and binary evolution.

A curvilinear nomogram of peak expiratory flow rate for the young.

OBJECTIVE: Peak expiratory flow rates (PEFRs) differ among populations and between times. The new EU scale of the mini-Wright flow-meter has been introduced since 2004. This study updated the PEFR nomograms with the new scale for Chinese children and adolescents (aged 6-19 years) in Hong Kong. METHODS: A convenience sample was recruited from 34 primary care practices (patients' companions/children) and four schools. Standardization workshops were run for the physicians, and the proper use of the flow-meter was demonstrated to students prior to the data collection. Brand new meters were used. For each sex, the linear regression model was used to determine the relationship between PEFR and the variables of age and body height. The open-source software PyNomo was used to generate the nomograms. RESULTS: After excluding 66 participants with past/current history of respiratory tract diseases, heart disease, incomplete data, and poor effort, PEFRs were collected from 798 males and 794 females. The PEFR had a linear relationship with age but a curvilinear relationship with height. The regression equations for predicted PEFR were ln(PEFR) = 1.810256*ln(height) + 0.038297*age - 3.734139 for males and ln(PEFR) = 1.525509*ln(height) + 0.033275*age - 2.368592 for females. The corresponding nomograms were constructed. They were tested with 230 patients in primary care; 9.6% (12 males and 10 females) had PEFR less than the predicted value by ≥20%. CONCLUSION: The body height was a stronger determinant than age for PEFR. The predicted PEFR with these determinants bear a curvilinear relationship.

Fighting tobacco smoking--a difficult but not impossible battle.

According to the World Health Organization (WHO), tobacco-related disease is the single largest preventable cause of death in the world today, killing around 5.4 million people a year--an average of one person every six seconds. The total number of death caused by tobacco consumption is higher than that of tuberculosis, HIV/AIDS and malaria combined. Unlike other communicable diseases, however, tobacco-related disease has a man-made consensus vector--the tobacco companies that play an active role to promote tobacco consumption, which directly heightens the disease morbidity. Any public health policy designed to curb smoking behavior has to prepare for opposite lobbying actions from tobacco companies that undermine the effects of the health measures. Another unique nature of the tobacco epidemic is that it can be cured, not by medicines or vaccines, but on the concerted actions of government and civil society. Many countries with a history of tobacco control measures indeed experienced a reduction of tobacco consumption. As most of these governments launched a range of measures simultaneously, it is hard to quantify the relative merits of different control strategies that contributed to the drop in the number of smokers. These packages of strategies can come in different forms but with some common features. Political actions with government support, funding, and protection are crucial. Without these, antismoking efforts in any part of the world are unlikely to be successful.

Atopic dermatitis complicated by methicillin-resistant Staphylococcus aureus infection.

INTRODUCTION: Staphylococcus aureus colonization/infection is commonly associated with disease severity in children with atopic dermatitis. The present report is a three-year retrospective chart review of five cases (comprising three boys and two girls, aged 9-15 years at referral) of methicillin-resistant S. aureus (MRSA) in children with moderate-to-severe atopic dermatitis. The review period spanned 2004-2007. All had longstanding severe disease, high IgE and eosinophil counts. Generalized erythema and a peculiar fishy odor were frequently observed by parents and physicians when MRSA was isolated during some of the episodes of exacerbation. All had tried various combinations of topical and systemic steroids, topical immunomodulants, traditional Chinese medicine and courses of antibiotics-without lasting relief. All specimens of MRSA had in-vitro sensitivity to vancomycin, with corresponding clinical correlates of disappearance of the erythema and fishy odor. CONCLUSION: A fishy odor and facial/generalized erythema in a patient with atopic dermatitis should alert the physician to screen for MRSA. The organism is rarely isolated, even among children with moderate-to-severe atopic dermatitis, and is usually sensitive to vancomycin.

Dominantly-inherited lop ears.

We describe a four-generation Chinese family that included five members who had an isolated bilateral lop ear anomaly. The presentation suggested a dominant mode of inheritance. The absence of male-to-male transmission does not exclude an X-linked dominant mode of inheritance. Since the phenotypic anomaly of the male proband was no more severe than the affected female members, an autosomal dominant mode of inheritance is most likely.