Wasting syndrome in neonatal mice after administration of salivary gland homogenate

Summary A wasting syndrome, similar to that occurring after cortisol treatment, was induced in neonatal mice by means of the daily i.p. administration of salivary gland homogenate: 24 h after a single injection of the, homogenate, profuse cell necrosis was observed in the thymic cortex, 48 h later the cortex was devoid of lymphocytes. It is hypothesized that the submandibular glands of mice contain substance which are capable of inducing a cortisol-like effect.We should like to thank Miss Angela Würfler for her careful technical assistance.     

Deficiency in renomedullary prostaglandin synthesis related to the evolution of essential hypertension

Summary Continued PG synthesis in the early stages of essential hypertension might reflect an activation of the renal antihypertensive function in respect to neurogenic and/or hormonal pression stimuli, subsequently a deficiency of renal PG synthesis related to irreversible changes with the kidney would lead to the prepoderance of a pressure mechanism, resulting to a further increase of blood pressure.We thank Dr.J. R. Pike of the Upjohn Company, Kalamazoo Michigan, who kindly provided PGs. This work was supported by a grant from INSERM (ATP 17 No. of contract73547917) to Dr.Papanicolaou.     

Laser-induced ultrafast spin reorientation in the antiferromagnet TmFeO3

All magnetically ordered materials can be divided into two primary classes: ferromagnets and antiferromagnets. Since ancient times, ferromagnetic materials have found vast application areas, from the compass to computer storage and more recently to magnetic random access memory and spintronics. In contrast, antiferromagnetic (AFM) materials, though representing the overwhelming majority of magnetically ordered materials, for a long time were of academic interest only. The fundamental difference between the two types of magnetic materials manifests itself in their reaction to an external magnetic field-in an antiferromagnet, the exchange interaction leads to zero net magnetization. The related absence of a net angular momentum should result in orders of magnitude faster AFM spin dynamics. Here we show that, using a short laser pulse, the spins of the antiferromagnet TmFeO3 can indeed be manipulated on a timescale of a few picoseconds, in contrast to the hundreds of picoseconds in a ferromagnet. Because the ultrafast dynamics of spins in antiferromagnets is a key issue for exchange-biased devices, this finding can expand the now limited set of applications for AFM materials.     

Atomic transient recorder

In Bohr's model of the hydrogen atom, the electron takes about 150 attoseconds (1 as = 10(-18) s) to orbit around the proton, defining the characteristic timescale for dynamics in the electronic shell of atoms. Recording atomic transients in real time requires excitation and probing on this scale. The recent observation of single sub-femtosecond (1 fs = 10(-15) s) extreme ultraviolet (XUV) light pulses has stimulated the extension of techniques of femtochemistry into the attosecond regime. Here we demonstrate the generation and measurement of single 250-attosecond XUV pulses. We use these pulses to excite atoms, which in turn emit electrons. An intense, waveform-controlled, few cycle laser pulse obtains 'tomographic images' of the time-momentum distribution of the ejected electrons. Tomographic images of primary (photo)electrons yield accurate information of the duration and frequency sweep of the excitation pulse, whereas the same measurements on secondary (Auger) electrons will provide insight into the relaxation dynamics of the electronic shell following excitation. With the current approximately 750-nm laser probe and approximately 100-eV excitation, our transient recorder is capable of resolving atomic electron dynamics within the Bohr orbit time.     

High-resolution record of Northern Hemisphere climate extending into the last interglacial period

Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 degrees C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time.     

Homozygous mutation of AURKC yields large-headed polyploid spermatozoa and causes male infertility

The World Health Organization conservatively estimates that 80 million people suffer from infertility worldwide. Male factors are believed to be responsible for 20-50% of all infertility cases, but microdeletions of the Y chromosome are the only genetic defects altering human spermatogenesis that have been reported repeatedly. We focused our work on infertile men with a normal somatic karyotype but typical spermatozoa mainly characterized by large heads, a variable number of tails and an increased chromosomal content (OMIM 243060). We performed a genome-wide microsatellite scan on ten infertile men presenting this characteristic phenotype. In all of these men, we identified a common region of homozygosity harboring the aurora kinase C gene (AURKC) with a single nucleotide deletion in the AURKC coding sequence. In addition, we show that this founder mutation results in premature termination of translation, yielding a truncated protein that lacks the kinase domain. We conclude that the absence of AURKC causes male infertility owing to the production of large-headed multiflagellar polyploid spermatozoa.     

Observation of coupled magnetic and electric domains

Ferroelectromagnets are an interesting group of compounds that complement purely (anti-)ferroelectric or (anti-)ferromagnetic materials--they display simultaneous electric and magnetic order. With this coexistence they supplement materials in which magnetization can be induced by an electric field and electrical polarization by a magnetic field, a property which is termed the magnetoelectric effect. Aside from its fundamental importance, the mutual control of electric and magnetic properties is of significant interest for applications in magnetic storage media and 'spintronics'. The coupled electric and magnetic ordering in ferroelectromagnets is accompanied by the formation of domains and domain walls. However, such a cross-correlation between magnetic and electric domains has so far not been observed. Here we report spatial maps of coupled antiferromagnetic and ferroelectric domains in YMnO3, obtained by imaging with optical second harmonic generation. The coupling originates from an interaction between magnetic and electric domain walls, which leads to a configuration that is dominated by the ferroelectromagnetic product of the order parameters.     

Attosecond control of electronic processes by intense light fields

The amplitude and frequency of laser light can be routinely measured and controlled on a femtosecond (10(-15) s) timescale. However, in pulses comprising just a few wave cycles, the amplitude envelope and carrier frequency are not sufficient to characterize and control laser radiation, because evolution of the light field is also influenced by a shift of the carrier wave with respect to the pulse peak. This so-called carrier-envelope phase has been predicted and observed to affect strong-field phenomena, but random shot-to-shot shifts have prevented the reproducible guiding of atomic processes using the electric field of light. Here we report the generation of intense, few-cycle laser pulses with a stable carrier envelope phase that permit the triggering and steering of microscopic motion with an ultimate precision limited only by quantum mechanical uncertainty. Using these reproducible light waveforms, we create light-induced atomic currents in ionized matter; the motion of the electronic wave packets can be controlled on timescales shorter than 250 attoseconds (250 x 10(-18) s). This enables us to control the attosecond temporal structure of coherent soft X-ray emission produced by the atomic currents--these X-ray photons provide a sensitive and intuitive tool for determining the carrier-envelope phase.     

On Mach on time

Mach's views on the nature of time have been unduly neglected. They are both more defensible in their own historical context and more relevant to our own contemporary context than has been appreciated. This essay provides an extended and comprehensive discussion of Mach's writings on time offering novel analysis and interpretation. Contra the prevailing current in the secondary literature, Mach's views on time are shown to be largely vindicated in the context of late nineteenth century physics. Then, building upon this more historical project, we conclude with a critical evaluation of the modern Machian view of time due to Barbour within the context of relativistic chronometry as instantiated via pulsar clocks and atomic clocks. Once more, considered analysis serves to support the Machian view. About time we go back to Mach.     

Three denials of time in the interpretation of canonical gravity

The analysis of the temporal structure of canonical general relativity and the connected interpretational questions with regard to the role of time within the theory both rest upon the need to respect the fundamentally dual role of the Hamiltonian constraints found within the formalism. Any consistent philosophical approach towards the theory must pay dues to the role of these constraints in both generating dynamics, in the context of phase space, and generating unphysical symmetry transformations, in the context of a hypersurface embedded within a solution. A first denial of time in the terms of a position of reductive temporal relationalism can be shown to be troubled by failure on the first count, and a second denial in the terms of Machian temporal relationalism can be found to be hampered by failure on the second. A third denial of time, consistent with both of the Hamiltonian constraints roles, is constituted by the implementation of a scheme for constructing observables in terms of correlations and leads to a radical Parmenidean timelessness. The motivation for and implications of each of these three denials are investigated.