Structure and Efficiency in Bacterial Photosynthetic Light Harvesting

Photosynthetic organisms use networks of chromophores to absorb sunlight and deliver the energy to reaction centres, where charge separation triggers a cascade of chemical steps to store the energy. We present a detailed model of the light-harvesting complexes in purple bacteria, including explicit interaction with sunlight; energy loss through radiative and non-radiative processes; and dephasing and thermalizing effects of coupling to a vibrational bath. An important feature of the model is that we capture the effect of slow vibrational modes by introducing time-dependent disorder. Our model describes the experimentally observed high efficiency of light harvesting, despite the absence of long-range quantum coherence. The one-exciton part of the quantum state fluctuates due to slow vibrational changes, but remains highly mixed at all times. This lack of long-range coherence suggests a relatively minor role for structure in determining the efficiency of bacterial light harvesting. To investigate this we built hypothetical models with randomly arranged chromophores, but still observed high efficiency when typical nearest-neighbour distances are comparable with those found in nature. This helps to explain the efficiency of energy transport in organisms whose chromophore networks differ widely in structure, while also suggesting new design criteria for efficient artificial light-harvesting devices

The weak password problem: chaos, criticality, and encrypted p-CAPTCHAs

Vulnerabilities related to weak passwords are a pressing global economic and security issue. We report a novel, simple, and effective approach to address the weak password problem. Building upon chaotic dynamics, criticality at phase transitions, CAPTCHA recognition, and computational round-off errors we design an algorithm that strengthens security of passwords. The core idea of our method is to split a long and secure password into two components. The first component is memorized by the user. The second component is transformed into a CAPTCHA image and then protected using evolution of a two-dimensional dynamical system close to a phase transition, in such a way that standard brute-force attacks become ineffective. We expect our approach to have wide applications for authentication and encryption technologies.Comment: 5 pages, 6 figer

The human health effects of exposure to polybrominated biphenyls

Polybrominated biphenyls (PBB) were inadvertently introduced into the food chain in Michigan in 1973. Fifty-one people with known exposure to PBB were studied. Twenty-three farmers with disabling health complaints, and 28 chemical workers involved in the PBB manufacturing process were systematically evaluated to determine if these highrisk groups suffered adverse effects from their known exposure to PBB. The farmers had a high frequency of constitutional symptoms, hepatomegaly and skin rashes, findings not commonly noted in the chemical workers. Biochemical and hematologic testing revealed few abnormalities, and electromyograms, nerve conduction velocities, endocrine studies, and lymphocyte transformation studies provided no objective findings that correlated with subjective complaints. There was no relationship between PBB levels and physical or laboratory abnormalities. Present evidence suggests that people exposed to PBB have few objective findings at this time, and reactive depression may be responsible for the high prevalence of constitutional symptoms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24421/1/0000692.pd

H-Bond Self-Assembly: Folding versus Duplex Formation

Linear oligomers equipped with complementary H-bond donor (D) and acceptor (A) sites can interact via intermolecular H-bonds to form duplexes or fold via intramolecular H-bonds. These competing equilibria have been quantified using NMR titration and dilution experiments for seven systems featuring different recognition sites and backbones. For all seven architectures, duplex formation is observed for homo-sequence 2-mers (AA·DD) where there are no competing folding equilibria. The corresponding hetero-sequence AD 2-mers also form duplexes, but the observed self-association constants are strongly affected by folding equilibria in the monomeric states. When the backbone is flexible (five or more rotatable bonds separating the recognition sites), intramolecular H-bonding is favored, and the folded state is highly populated. For these systems, the stability of the AD·AD duplex is 1-2 orders of magnitude lower than that of the corresponding AA·DD duplex. However, for three architectures which have more rigid backbones (fewer than five rotatable bonds), intramolecular interactions are not observed, and folding does not compete with duplex formation. These systems are promising candidates for the development of longer, mixed-sequence synthetic information molecules that show sequence-selective duplex formation.We thank the Engineering and Physical Sciences Research Council (EP/J008044/2) and European Research Council (ERC-2012-AdG 320539-duplex) for funding

Reporting of conflicts of interest in guidelines of preventive and therapeutic interventions

BACKGROUND: Guidelines published in major medical journals are very influential in determining clinical practice. It would be essential to evaluate whether conflicts of interests are disclosed in these publications. We evaluated the reporting of conflicts of interest and the factors that may affect such disclosure in a sample of 191 guidelines on therapeutic and/or preventive measures published in 6 major clinical journals (Annals of Internal Medicine, BMJ, JAMA, Lancet, New England Journal of Medicine, Pediatrics) in 1979, 1984, 1989, 1994 and 1999. RESULTS: Only 7 guidelines (3.7%) mentioned conflicts of interest and all were published in 1999 (17.5% (7/40) of guidelines published in 1999 alone). Reporting of conflicts of interest differed significantly by journal (p=0.026), availability of disclosure policy by the journal (p=0.043), source of funding (p < 0.001) and number of authors (p=0.004). In the entire database of 191 guidelines, a mere 18 authors disclosed a total of 24 potential conflicts of interest and most pertained to minor issues. CONCLUSIONS: Despite some recent improvement, reporting of conflicts of interest in clinical guidelines published in influential journals is largely neglected

MS care: integrating advanced therapies and holistic management

Lifestyle and environmental factors are key determinants in disease causality and progression in neurological conditions, including multiple sclerosis (MS). Lack of exercise, poor diet, tobacco smoking, excessive alcohol intake, social determinants of health, concomitant medications, poor sleep and comorbidities can exacerbate MS pathological processes by impacting brain health and depleting neurological reserves, resulting in more rapid disease worsening. In addition to using disease-modifying therapies to alter the disease course, therapeutic strategies in MS should aim to preserve as much neurological reserve as possible by promoting the adoption of a “brain-healthy” and “metabolically-healthy” lifestyle. Here, we recommend self-regulated lifestyle modifications that have the potential to improve brain health, directly impact on disease progression and improve outcomes in people with MS. We emphasise the importance of self-management and adopting a multidisciplinary, collaborative and person-centred approach to care that encompasses the healthcare team, family members and community support groups