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Nature 502, 346–349 (2013); doi:10.1038/nature12569 In this Letter, we have identified an important error affecting Fig. 4 and Extended Data Fig. 6, as well as the values of some parameters derived from our model fits. We stress that this error in no way affects the discussion or the conclusions. Inbuilding the bolometric light curve of the superluminous supernova PTF 12dam, our code assumed that photometry from the Swift satellite was calibrated in the Vega magnitude system.

The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies. Previous candidate flares have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two `relativistic' candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet. Here we report the discovery of a luminous ultraviolet-optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decline of its light curve follows the predicted mass accretion rate, and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about 2 million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core., Comment: To appear in Nature on May 10, 2012

IN man foetal haemoglobin (Hb F, α2γ2), which is the main respiratory protein throughout intrauterine life, is almost completely replaced by adult haemoglobin (Hb A, α2β2) during the first 6 months after birth. The mechanism of the switch from γ to β-chain production is unknown. In intra uterine life erythropoiesis occurs first in the yolk sac, then in the liver and spleen and finally in the bone marrow1. Hb A production occurs at a low level from about the ninth to twelfth week of gestation2–6 and there is evidence that foetal liver can synthesize both Hb A and F4,7. It is not known, however, whether the switch from Hb F to Hb A production is synchronous in different foetal organs, which might be expected if it were hormonally controlled, or whether there are local organ-specific differences in the rate of change from Hb F to A production. To examine this problem, and to obtain further information about the pattern of Hb A production in early intrauterine life, we have examined Hb synthesis in foetal organs at different stages of development.

DURING human development changes occur in the red-cell proteins and antigens1. At birth the predominant haemoglobin (Hb) is Hb F with approximately 20% and less than 1% of the major and minor adult haemoglobin components (Hbs A and A2) respectively. Hb F at birth is a mixture of two molecular species, one with glycine at position 136 of the γ chain (α2γ2136Gly) and the other with alanine at this position (α2γ2136Ala). The γ chains are designated Gγ and Aγ respectively and at birth the ratio of Gγ/Aγ is approximately 3 : 1 (ref. 2). Foetal red cells contain low levels of carbonic anhydrase isozymes B and C and react strongly with anti-i antibody but weakly with anti-I. During the first 12 months the level of Hb F falls and it is replaced by Hbs A and A2. The ratio of Gγ/Aγ chains changes to 2 : 3 in the small amount of Hb F found in adult life3. The red cells lose their reactivity to i antibody and increase their reactivity to I. The carbonic anhydrase isozymes increase to adult levels by the end of the third year4. These changes act as markers for the change from foetal to adult erythropoiesis.

IT is well established that physical exercise causes an increase in sympathetic activity, as shown by rises in the levels of plasma and urine catecholamines1. This increase in endogenous adrenergic activity can be used to study the effects of sympathetic stimulation. Such studies usually compare a control situation with one in which either α or β adrenergic receptor activity is blocked pharmacologically, thereby allowing study of both the blocked and unblocked receptors. Beta blocking drugs have been used in this way to study changes in carbohydrate metabolism2, free fatty acid metabolism3, and blood coagulation and fibrinolysis4 induced by exercise.

Haemoglobin E (alpha 2 beta 2(26)Glu leads to Lys) is one of the commonest haemoglobin variants. There are an estimated 30 million carriers of the beta E gene in South-East Asia, where they comprise more than 50% of the population in some areas; however, the reasons for this high frequency have never been adequately explained. Homozygotes for HbE may be midly anaemic, but they do not have any clinical disability. However, individuals heterozygous for both beta E and beta thalassaemia (HbE/beta thalassaemia) have a severe clinical disorder which in some cases may approach that seen in homozygous beta thalassaemia and which is by far the commonest form of symptomatic thalassaemia in the Indian subcontinent and South-East Asia. Haemoglobin E is the only common structural variant which interacts with beta thalassaemia to produce a severe disorder and the underlying mechanism of the interaction is not known. We have studied several homozygotes and heterozygotes for HbE and show here that the beta E chain is inefficiently synthesized and produces the phenotype of a mild form of beta thalassaemia; hence, when inherited together with beta thalassaemia it causes a marked beta-chain deficit. Furthermore, the mechanism for the defective production of beta E chains seems to be a reduction of beta E mRNA, a most unexpected finding in a disorder caused by a single amino acid substitution and presumably by a single nucleotide change in the DNA of the beta globin gene.

We consider here some of the consequences of adiabatic dynamically driven motions within the radiative inner region of the Sun and solar-type stars for which it is assumed that an oblique magnetic field is trapped below the convection zone. The internal motions are due to both centrifugal and magnetic forces and we discuss their behaviour over the lifetime of a solar-type star. We assume, following Mestel1, that stars of mass ∼1 M⊙ have a magnetic field which is contained by the outer convection zones of solar-type stars. We propose that if such a field exists in the interior of the Sun and other solar-type stars then coupled with the possibility of a rapidly rotating core as suggested by Claverie et al.2, we have a possible mechanism for diffusive-type motions which could influence solar models3. Furthermore, we show that if the nutation frequency of an oblique magnetic rotator corresponds to the solar cycle then the magnetic field will need to be of the order of 107 G. All of the relevant theory and equations may be found in refs 4 and 5 and here we merely outline some of the pertinent assumptions and results contained therein.

IT has been shown previously that progressive deformation of an annealed metal breaks down the grains into smaller units, or crystallites, which have a minimum size characteristic of the metal1,2. The lower limiting size for metals so far examined lies in the range 10-4 to 10-6 cm. A precise determination of this size has become of importance, because it appears to coincide with the maximum strength developed during deformation of the metal3.

THE changes in crystalline texture of metals subjected to plastic deformation can be studied by following the increase in diffusion of the X-ray reflexions from the atomic planes. The correct procedure should be always to obtain the reflexions direct from the metal in the normal solid state. But for convenience much work has been based on the circular camera technique, where the test specimen has to be in the form of powder. The metal has been reduced to powder by filing, and measurements made of the breadth and intensity of the X-ray reflexions from the filings. These values have been compared with the breadth and intensity of the reflexions after the filings have been annealed and the effect of deformation thereby removed. The difference has been taken to represent the effect of the cold plastic deformation produced by the action of filing. Then it has been assumed that the same differences would exist between the annealed and plastically deformed state in the solid metal ; also that the theoretical conclusions would be applicable directly to interpretation of the structural changes produced by plastic deformation of the solid metal.

ARISING from the recent communication by Prof. W.T. Astbury and Mr. C. J. Brown1 concerning the structure of 'Terylene', we wish to place on record the earliest investigation of its structure by the X-ray method. The results recently reported by Astbury and Brown from work done in 1944 are in general agreement with those which we obtained some two years earlier.

IT is thought that the experimental observation described in the present note leads to new and useful information on the mechanism of creep in metals, a problem which was the subject of a recent conference at the Royal Society1.

THE process of cold-rolling or drawing certain metals is known to produce a permanent irregular departure from the normal atomic structure of the grains. I find that this type of lattice distortion occurs also in wires of constantan which have been stretched longitudinally by gradual loading. The degree of the distortion increases most rapidly as the yield-point is approached. Nickel, copper, and most alloys examined give similar results.

IN recent work on the deformation and fracture of metals under static and fatigue tests, it was shown that originally perfect grains were systematically dispersed into crystallites. The interesting feature of the process was the appearance of a lower limiting size, about 10-5cm., below which the crystallites could not be broken down further by the modes of deformation employed1.

THE late Mr. Campbell Swinton observed (Proc. Roy. Soc., 61, 79; 1897) that a carbon anticathode in a gas X-ray tube under certain conditions showed a ring of fluorescence which he considered due to the hollow nature of the cathode stream. The following preliminary account of some experiments with a gas X-ray tube of the Shearer type shows that the effect can be more complex than is usually suspected.

X-RAY analysis in the steel industry formed the subject of a conference organised by the X-Ray Analysis Graup of the Institute of Physics, and held at Sheffield on November 8 and 9. Dr. W. H. Taylor presided over a well-attended meeting.

WE have attempted to study the process of resinification by following with the aid of X-ray diffraction the transitional stages of structure taking place in an initially crystalline compound which on heating forms a resin. Well-known substances of this type are the phenolic alcohols, which on heating form the class of resins termed 'saliretins'. A first result of the X-ray method has been to show that p-cresol monoalcohol (2-hydroxy-methyl-4-methylphenol) changes over at an intermediate stage to an apparently new compound to which this note directs attention.

IN his book “Applied X-Rays” Dr. G. L. Clark publishes some very interesting photographs showing the connexion between the magnetic hysteresis loss and the grain size of 4 per cent silicon steels. He takes the grain size to be inversely proportional to the number of spots produced under given conditions on a Laue photograph, and quotes a formula connecting this number with the magnetic hysteresis loss of the steel. The fewer the Laue spots, the less is the hysteresis loss.

A PROBLEM in X-ray diffraction has been the diffusion of the X-ray reflexions from a metal which has been subjected to plastic deformation. A crucial experiment has long been called for which would indicate clearly what modifications in structure of the deformed metal are mainly responsible for the effect. The method usually suggested is indecisive : it involves a laborious measurement of changes scarcely greater than experimental error, and, as recent publications have shown, gives different results in the hands of different workers1,2. It may be of interest, therefore, to record an alternative method which, for a number of metals, including iron and steel, appears to solve the problem in a simple direct manner.

WHEN a metal is cold-worked, its X-ray spectrum is modified. In most cases, this modification includes a diffusion of the diffraction lines. If the diffused lines are photographed in an X-ray camera giving high dispersion, and analysed with the aid of a rnicrophotometer, it is found that, in general, the broadening does not take place symmetrically about the normal position of the line.

X-RAY analysis of metals affords a means of detecting the type of internal strain which is accompanied by distortion of the crystal lattice. The distortion is reflected in the X-ray diffraction photographs in that it causes a broadening of the spectrum lines; the effect has been noted for metals which have been cold-worked or which contain a highly dispersed solute.

THE technical application of metals involves a detailed knowledge of their behaviour under external stresses. In the usual method of testing, measurements are made of the changes in external dimensions of a test piece when stresses of known magnitude are applied, as in the determination of the elementary load extension diagram. It is nowadays practicable, however, by use of modern X-ray diffraction technique, to obtain simultaneously with the external load-extension diagram the analogous diagram for the atomic lattice itself, in which direct measurements are made of the displacements of the atoms from their normal positions under stress and of their recovery when the applied stress is removed.

Messrs. M. C. Shaw and C. D. Strang1 have criticized the thermal wedge explanation of the parallel surface thrust bearing put forward by A. Fogg in his paper2 describing his experimental work.

IN recently published work1, I have shown that the cold-working of most metals produces, first, a stage of crystal disruption which is accompanied by growth of lattice distortion, and then, after the lattice distortion limit is reached, the second stage in which the crystallites take up a preferred orientation. Normally, therefore, a metal which possesses this fibre structure also exhibits lattice distortion.

The accompanying photographs (Fig. 1) show an interesting example of a case where the relative intensities of the lines in any X-ray spectrum may vary without a corresponding change in atomic arrangement. They are Debye photographs of chromium plated wires obtained under different conditions of electrodeposition. It is seen at once that the intensity of the middle line, the (200) reflection, in comparison with that of the other two lines, the (110) and (211), is as strong as normally it should be in the top photograph. In the second photograph it has become relatively weak. In the bottom photograph it has disappeared entirely.

IN experiments on the sorption of gases by zeolites, it has been shown1 that, of seven samples of chabazite found in different localities, one showed a much smaller power of sorption than all the others. It was supposed that the cause of this peculiar behaviour of this one sample might be sought in its higher univalent ion (K+, Na+) content, in contrast to the probable higher Ca+ +-content of the other chabazites. We have therefore tried to find the relation between the power of sorption of chabazite and its ionic content. This was done by comparing the sorption of different gases by samples of natural chabazite from Rubendorfel (near Aussig, Czechoslovakia) which had been boiled for two hundred hours in solutions containing K+, Na+, Ca++, Sr++, Ba++, Cd++, or La+++ -ions, in which way we hoped to obtain chabazites containing these ions. The sorbing power of samples so treated differed markedly from that of the original mineral, especially in the case of Na and Kpreparations.

AMONG the “Notes” in NATURE, vol. xv., p. 244, there is a description of a large meteor, of which I was fortunate enough to secure a good observation; but on comparing the apparent path, as observed by myself, with that recorded in the paragraph, I find the latter somewhat imperfect; the apparent path, as seen from near London, seems to have been curtailed both at beginning and at end of flight; probably the observer in question could further amplify his remarks, or some other correspondent send an observation. The following is an abstract from my note-book:—

IN a notice by Dr. A. B. Meyer in No. 116, vol. v. of NATURE, respecting earthquakes in the Island of Celebes, he states that the often-repeated story of the keepers of permanent magnets detaching themselves, and falling at the moment of an earthquake shock, was never verified in his experience. If I remember rightly, this peculiar action was first mentioned by a Frenchman living on the west coast of South America, and much doubted by many at the time. It is not likely that there is any difference between the effect of an American and an Asiatic earthquake on the magnet, if any such exists; but I must state, in corroboration of Dr. Meyer's note, that I have had a permanent magnet and keeper suspended in my study for many years, expressly for the purpose of testing this matter, and on no occasion of an earthquake has the keeper fallen from the magnet, not even in the terrific earthquake of 1863, which was so destructive to the city of Manila and the neighbouring provinces.