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The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant (B.1.1.529) rapidly replaced Delta (B.1.617.2) to become dominant in England. Our study assessed differences in transmission between Omicron and Delta using two independent data sources and methods. Omicron and Delta cases were identified through genomic sequencing, genotyping and S-gene target failure in England from 5–11 December 2021. Secondary attack rates for named contacts were calculated in household and non-household settings using contact tracing data, while household clustering was identified using national surveillance data. Logistic regression models were applied to control for factors associated with transmission for both methods. For contact tracing data, higher secondary attack rates for Omicron vs. Delta were identified in households (15.0% vs. 10.8%) and non-households (8.2% vs. 3.7%). For both variants, in household settings, onward transmission was reduced from cases and named contacts who had three doses of vaccine compared to two, but this effect was less pronounced for Omicron (adjusted risk ratio, aRR 0.78 and 0.88) than Delta (aRR 0.62 and 0.68). In non-household settings, a similar reduction was observed only in contacts who had three doses vs. two doses for both Delta (aRR 0.51) and Omicron (aRR 0.76). For national surveillance data, the risk of household clustering, was increased 3.5-fold for Omicron compared to Delta (aRR 3.54 (3.29–3.81)). Our study identified increased risk of onward transmission of Omicron, consistent with its successful global displacement of Delta. We identified a reduced effectiveness of vaccination in lowering risk of transmission, a likely contributor for the rapid propagation of Omicron.
Neurosurgical services in the UK are organised regionally into 34 acute neuroscience centres. Brain injury, both traumatic and non-traumatic, is common, and patients often present to local hospitals requiring further treatment in a neuroscience centre. Between April 2014 and June 2015, 15 820 patients suffered a traumatic brain injury in the UK. Of these, 6258 were transferred directly to a neuroscience centre, 5880 were not admitted to a neuroscience centre and 3682 underwent a secondary transfer from the admitting hospital to a neuroscience centre.1 In addition to traumatic brain injury, indications for non-traumatic causes of brain injury requiring acute transfer to a neuroscience centre continue to increase.
Glaciers and ice caps around the world are changing quickly, with surge-type behaviour superimposed upon climatic forcing. Here, we study Iceland's second largest ice cap, Langjökull, which has both surge- and non-surge-type outlets. By differencing elevation change with surface mass balance, we estimate the contribution of ice dynamics to elevation change. We use DEMs, in situ stake measurements, regional reanalyses and a mass-balance model to calculate the vertical ice velocity. Thus, we not only compare the geodetic, modelled and glaciological mass balances, but also map spatial variations in glacier dynamics. Maps of emergence and submergence velocity successfully highlight the 1998 surge and subsequent quiescence of one of Langjökull's outlets by visualizing both source and sink areas. In addition to observing the extent of traditional surge behaviour (i.e. mass transfer from the accumulation area to the ablation area followed by recharge of the source area), we see peripheral areas where the surge impinged upon an adjacent ridge and subsequently retreated. While mass balances are largely in good agreement, discrepancies between modelled and geodetic mass balance may be explained by inaccurate estimates of precipitation, saturated adiabatic lapse rate or degree-day factors. Nevertheless, the study was ultimately able to investigate dynamic surge behaviour in the absence of in situ measurements during the surge.
Protozoan parasites are fearsome pathogens responsible for a
substantial proportion of human mortality, morbidity, and economic
hardship. The principal disease agents are members of the orders
Apicomplexa (Plasmodium, Toxoplasma, Eimeria) and Kinetoplastida
(Trypanosomes, Leishmania). The majority of humans are at risk from
infection from one or more of these organisms, with profound effects on
the economy, social structure and quality of life in endemic areas;
Plasmodium itself accounts for over one million deaths per annum, and
an estimated 4 × 107 disability-adjusted life years
(DALYs), whereas the Kinetoplastida are responsible for over 100,000
deaths per annum and 4 × 106 DALYs. Current control
strategies are failing due to drug resistance and inadequate
implementation of existing public health strategies. Trypanosoma
brucei, the African Trypanosome, has emerged as a favored model
system for the study of basic cell biology in Kinetoplastida, because
of several recent technical advances (transfection, inducible
expression systems, and RNA interference), and these advantages,
together with genome sequencing efforts are widely anticipated to
provide new strategies of therapeutic intervention. Here we describe a
suite of methods that have been developed for the microscopic analysis
of T. brucei at the light and ultrastructural levels, an
essential component of analysis of gene function and hence
identification of therapeutic targets.
An atom consists of a positively charged nucleus, together with a number of negatively charged electrons. Inside the nucleus there are protons, each of which carries positive charge e, and neutrons, which have no charge. So the charge on the nucleus is Ze, where Z, the atomic number, is the number of protons. The charge on each electron is -e, so that when the atom has Z electrons it is electrically neutral. If some of the electrons are stripped off, the atom then has net positive charge; it has been ionised.
The electrons are held in the atom by the electrostatic attraction between each electron and the nucleus. There is also an attraction because of the gravitational force, but this is about 10-40 times less strong, and so may be neglected. The protons and neutrons are held together in the nucleus by a different type of force, the nuclear force. The nuclear force is much stronger than the electrical force, and its attraction more than counteracts the electrostatic repulsion between pairs of protons. The nuclear force does not affect electrons. It is a very short-range force, so that it keeps the neutrons and protons very close together; the diameter of a nucleus is of the order of 10-15 m. By contrast, the diameter of the whole atom is about 10-10 m, so that for many purposes one can think of the nucleus as a point charge.
This book is intended as a first course on quantum mechanics and its applications. It is designed to be a first course rather than a complete one, and it is based on lectures given to mathematics and physics students in Cambridge. The book should be suitable also for engineering students.
The first five chapters deal with basic quantum mechanics, and are followed by a revision quiz to test the reader's understanding of them. The remaining chapters concentrate on applications. In most courses on quantum mechanics, the first application is to scattering problems. While recognising the importance of scattering theory, we have chosen rather to describe the application of quantum mechanics to physical phenomena that are of more everyday interest. These include molecular binding, the physics of masers and lasers, simple properties of crystalline solids arising from their electronic band structure, and the operation of junction transistors.
A few problems are included at the end of each chapter. We urge the student to work through all of these, as they form an integral part of the course. Some hints on their solution may be found at the end of the book.
A previous edition of this book was published under the title Simple Quantum Physics in 1979. In this new edition, the main change is the addition of a chapter on the theory of spin, and its application to magnetic resonance imaging. We have also described the WKB approximation and its application to a-decay, and have made a number of other minor changes.
In chapter 5 we saw how in quantum mechanics electrons are bound to nuclei so as to form atoms. We now give a rather abbreviated account of how atoms bind together to form molecules. There is more than one type of molecular binding. We shall confine our discussion to the type known as covalent binding. The possibility of this type of binding relies on an effect that is peculiar to quantum mechanics, the tunnel effect, which we have already encountered in chapter 3.
The ionised hydrogen molecule
The simplest molecule is the ionised hydrogen molecule, which consists of two protons and one electron. The Coulomb force between the two protons tends to push them apart; we investigate how the presence of the electron overcomes this repulsion and holds the molecule together.
An exact calculation is difficult, but we can discuss the general features of the bonding by making suitable approximations. As the protons are much heavier than the electron, we may neglect their motion compared with that of the electron, and so regard them as fixed. We show that the expectation value of the energy, considered as a function of the proton separation R, has a minimum for a certain value of R, so that there is a stable equilibrium configuration.
Suppose first that R is so large that in the vicinity of each of the protons the Coulomb field of the other is completely negligible.