Picometer scale imaging of the valence electron potential of solids

Die Verteilung der Dichte der Valenzelektronen in Materialien definiert deren chemische, optische und biologische Eigenschaften. Daher ist die direkte Darstellung von Valenzelektronen in Festkörpern von höchster Wichtigkeit. Röntgenelektronen- und Neutronenbeugung liefern essentielle Informationen über die atomaren Positionen in Materialien, aber versagen bei der Messung der Dichte der Valenzelektronen. Diese Arbeit konzentriert ihre Bestrebungen auf dieses essentielle Problem. Durch die Erzeugung Hoher-Harmonischer in Gasen konnten bereits erfolgreich die Bewegungen von Molekülorbitalen dargestellt und Valenzelektronenbewegungen gemessen werden. Die kürzliche Entdeckung Hoher-Harmonischer in kondensierter Materie stellt daher ein vielversprechend Mittel dar, um dieses Potential auch auf Festkörper auszuweiten. Durch die Verwendung starker Laserfelder, die Elektronen in Festkörpern auslenken, und durch die Messung ihrer hohen-harmonischen Emissionsspektren, welche aus der Streuung der Elektronen mit dem periodischen Potential resultieren, versuchen wir das periodische Valenzpotential von Festkörpern zu entschlüsseln. Es wird diskutiert, dass unter dem Einfluss starker Felder und der hoch-frequenten Anregung von Festkörpern sich Valenzelektronen im Laserfeld wie nahezu freie Teilchen verhalten und dass das periodische Potential lediglich eine schwache Störung ihrer Bewegung darstellt. Dies erlaubt es, bereits entwickelte kinematische Modelle auszuweiten, um die Erzeugung Hoher-Harmonischer zu beschreiben und ihre Charakteristiken wie die Cutoff- Energie und Intensität mit dem periodischen Potential und der Elektronendichte des Festkörpers zu verknüpfen. Diese Arbeit zeigt theoretisch und beweist experimentell, dass die Cutoff-Energie der hoch-harmonischen Emission es nun erstmalig erlaubt, den ionischen und den kovalenten Radius von Atomen in einem Kristall direkt zu bestimmen. Des Weiteren zeigt sie, dass die Messung der Intensitätsausbeute der Hohen-Harmonischen in Abhängigkeit der Anregungsstärke und für verschiedene Kristallwinkel die gesamte Rekonstruktion des periodischen Potentials und der Elektronendichte im Festkörper erlaubt. Diese Technik erlaubt es somit zum ersten Mal, das “Phasenproblem“ zu adressieren. Hohe-Harmonische, die vom Festkörper ausgehen, verkörpern Informationen über die Amplitude und die Phase der Fourier-Komponenten des periodischen Potentials. Das Potential zweier kristalliner Materialien, MgF2 und CaF2, konnte so mit einer Auflösung besser als 50pm rekonstruiert werden. Studien mehrerer Materialien wie SiO2, Diamant, MgO, SiC, und ZnO erlauben es, die Maßstäbe der neuen Mikroskopietechnik zu setzen.The valence electron density distribution of materials determine their chemical, optical, electronic and biological properties. Hence the direct imaging of valence electrons in solids is of paramount importance. X-ray, electron and neutron diffraction provide essential information about the position of atoms in materials but fail to probe the valence electron density. This thesis attempts to solve this essential problem. The technique of high harmonic generation in gases have successfully imaged molecular orbital and has allowed observation of valence electron motion. The recent discovery of high harmonic generation (HHG) in condensed matter systems holds promise for extending this capability in solids. Using strong laser fields to drive electrons in the bulk of a material and by recording high harmonics emitted as a result of the scattering of electrons by the periodic potential we attempt to decipher the valence electron potential of solids. It is argued that under the strong field and high-frequency driving of solids, valence electrons can be treated as nearly free particles in the laser field and that the periodic potential contributes only a weak perturbation in their motion. That allows extending the earlier developed kinematic models to describe the high harmonic generation and to link, their characteristics, such as cutoff energy and intensity with the periodic potential and the electron density of the solid. The thesis shows theoretically and proves experimentally that the cutoff energy of the high harmonic emission allows for the first time the direct probe of the ionic and covalent radius of atoms inside the crystal. Moreover, it shows that by recording the intensity yield of high harmonics versus the driving strength for various angles of the crystal permits the complete reconstruction of the periodic potential and electron density inside the solid. The technique allows addressing for the first time the "phase problem". High harmonics emanating from the crystal embody information about the amplitude and the phase of the Fourier components of the periodic potential. For two crystalline materials MgF2, and CaF2 the potential is reconstructed with a resolution better than 50 pm. The study of more materials such as SiO2, Diamond, MgO, SiC, and ZnO allows benchmarking the new microscopy technique

Effects of ecological and developmental factors on the heat shock response

This article does not have an abstract

Picometer scale imaging of the valence electron potential of solids

Die Verteilung der Dichte der Valenzelektronen in Materialien definiert deren chemische, optische und biologische Eigenschaften. Daher ist die direkte Darstellung von Valenzelektronen in Festkörpern von höchster Wichtigkeit. Röntgenelektronen- und Neutronenbeugung liefern essentielle Informationen über die atomaren Positionen in Materialien, aber versagen bei der Messung der Dichte der Valenzelektronen. Diese Arbeit konzentriert ihre Bestrebungen auf dieses essentielle Problem. Durch die Erzeugung Hoher-Harmonischer in Gasen konnten bereits erfolgreich die Bewegungen von Molekülorbitalen dargestellt und Valenzelektronenbewegungen gemessen werden. Die kürzliche Entdeckung Hoher-Harmonischer in kondensierter Materie stellt daher ein vielversprechend Mittel dar, um dieses Potential auch auf Festkörper auszuweiten. Durch die Verwendung starker Laserfelder, die Elektronen in Festkörpern auslenken, und durch die Messung ihrer hohen-harmonischen Emissionsspektren, welche aus der Streuung der Elektronen mit dem periodischen Potential resultieren, versuchen wir das periodische Valenzpotential von Festkörpern zu entschlüsseln. Es wird diskutiert, dass unter dem Einfluss starker Felder und der hoch-frequenten Anregung von Festkörpern sich Valenzelektronen im Laserfeld wie nahezu freie Teilchen verhalten und dass das periodische Potential lediglich eine schwache Störung ihrer Bewegung darstellt. Dies erlaubt es, bereits entwickelte kinematische Modelle auszuweiten, um die Erzeugung Hoher-Harmonischer zu beschreiben und ihre Charakteristiken wie die Cutoff- Energie und Intensität mit dem periodischen Potential und der Elektronendichte des Festkörpers zu verknüpfen. Diese Arbeit zeigt theoretisch und beweist experimentell, dass die Cutoff-Energie der hoch-harmonischen Emission es nun erstmalig erlaubt, den ionischen und den kovalenten Radius von Atomen in einem Kristall direkt zu bestimmen. Des Weiteren zeigt sie, dass die Messung der Intensitätsausbeute der Hohen-Harmonischen in Abhängigkeit der Anregungsstärke und für verschiedene Kristallwinkel die gesamte Rekonstruktion des periodischen Potentials und der Elektronendichte im Festkörper erlaubt. Diese Technik erlaubt es somit zum ersten Mal, das “Phasenproblem“ zu adressieren. Hohe-Harmonische, die vom Festkörper ausgehen, verkörpern Informationen über die Amplitude und die Phase der Fourier-Komponenten des periodischen Potentials. Das Potential zweier kristalliner Materialien, MgF2 und CaF2, konnte so mit einer Auflösung besser als 50pm rekonstruiert werden. Studien mehrerer Materialien wie SiO2, Diamant, MgO, SiC, und ZnO erlauben es, die Maßstäbe der neuen Mikroskopietechnik zu setzen.The valence electron density distribution of materials determine their chemical, optical, electronic and biological properties. Hence the direct imaging of valence electrons in solids is of paramount importance. X-ray, electron and neutron diffraction provide essential information about the position of atoms in materials but fail to probe the valence electron density. This thesis attempts to solve this essential problem. The technique of high harmonic generation in gases have successfully imaged molecular orbital and has allowed observation of valence electron motion. The recent discovery of high harmonic generation (HHG) in condensed matter systems holds promise for extending this capability in solids. Using strong laser fields to drive electrons in the bulk of a material and by recording high harmonics emitted as a result of the scattering of electrons by the periodic potential we attempt to decipher the valence electron potential of solids. It is argued that under the strong field and high-frequency driving of solids, valence electrons can be treated as nearly free particles in the laser field and that the periodic potential contributes only a weak perturbation in their motion. That allows extending the earlier developed kinematic models to describe the high harmonic generation and to link, their characteristics, such as cutoff energy and intensity with the periodic potential and the electron density of the solid. The thesis shows theoretically and proves experimentally that the cutoff energy of the high harmonic emission allows for the first time the direct probe of the ionic and covalent radius of atoms inside the crystal. Moreover, it shows that by recording the intensity yield of high harmonics versus the driving strength for various angles of the crystal permits the complete reconstruction of the periodic potential and electron density inside the solid. The technique allows addressing for the first time the "phase problem". High harmonics emanating from the crystal embody information about the amplitude and the phase of the Fourier components of the periodic potential. For two crystalline materials MgF2, and CaF2 the potential is reconstructed with a resolution better than 50 pm. The study of more materials such as SiO2, Diamond, MgO, SiC, and ZnO allows benchmarking the new microscopy technique

The vicious circle of poor science, poor journals and poor recognition

This article does not have an abstract

Forty years of the 93D puff of Drosophila melanogaster

The 93D puff of Drosophila melanogaster became attractive in 1970 because of its singular inducibility by benzamide and has since then remained a major point of focus in my laboratory. Studies on this locus in my and several other laboratories during the past four decades have revealed that (i) this locus is developmentally active, (ii) it is a member of the heat shock gene family but selectively inducible by amides, (iii) the 93D or heat shock RNA omega (hsrω) gene produces multiple nuclear and cytoplasmic large non-coding RNAs (hsrω-n, hsrω-pre-c and hsrω-c), (iv) a variety of RNA-processing proteins, especially the hnRNPs, associate with its >10 kb nuclear (hsrω-n) transcript to form the nucleoplasmic omega speckles, (v) its genomic architecture and hnRNP-binding properties with the nuclear transcript are conserved in different species although the primary base sequence has diverged rapidly, (vi) heat shock causes the omega speckles to disappear and all the omega speckle associated proteins and the hsrω-n transcript to accumulate at the 93D locus, (vii) the hsrω-n transcript directly or indirectly affects the localization/stability/activity of a variety of proteins including hnRNPs, Sxl, Hsp83, CBP, DIAP1, JNK-signalling members, proteasome constituents, lamin C, ISWI, HP1 and poly(ADP)-ribose polymerase and (viii) a balanced level of its transcripts is essential for the orderly relocation of various proteins, including hnRNPs, RNA pol II and HP1, to developmentally active chromosome regions during recovery from heat stress. In view of such multitudes of interactions, it appears that large non-coding RNAs like those produced by the hsrω gene may function as hubs to coordinate multiple cellular networks and thus play important roles in maintenance of cellular homeostasis

India's ambitions to be a world leader in S&T depend upon a drastic overhaul of the university system

This article does not have an abstract

Playing ‘The Floor is Lava’ in Real Life

The popular children’s game ‘the floor is lava’ seems entertaining when played using only the imagination, but it is not widely known what the effects would be if this game were to be played using real lava. This paper investigates whether playing this game in real life would be possible and what effect that would have on the human body.

Functional organization of polytene X-chromosome in two X-chromosome inversion carrying larvae of Drosophila melanogaster reared at 24°C or 10°C

Larvae of D. melanogasler carrying either the In(I)BM1 or In(I)BM2 inversion have been reared at 24° or at 10°C to study the morphology, transcription and replication of the X-chromosome in the salivary gland polytene nuclei. These two inversions share a similar left-hand breakpoint in euchromatin (16A 2-5 region in polytene X-chromosome) but have different right-hand breakpoints in the proximal heterochromatin. In 10°C reared BM1 male larvae, the polytene X appears somewhat more diffused than in 24°C reared larvae. On an average, in 36% of the polytene nuclei of 10°C reared BM2 male larvae the single X-chromosome appears considerably shortened in length, enlarged in width and has very indistinct band, while the other nucIei show "normal-looking" X as in BM1 larvae. This highly disorganized form of X-chromosome, referred to as "pompon-Iike" X, is never seen in cold-reared female or in warm-reared female as well as male BM2 or BM1 larvae. Hoechst 33258 fluorescence reveals that the "pompon-like" morphology of the X is due to loose packing of chromatin in different band regions. It is suggested that the "pompon-like" morphology is due to position effect variegation associated with the particular heterochromatin breakpoint in the BM2 inversion, 3H-uridine and 3H-thymidine labelling and autoradiography of polytene nuclei from cold-reared male and femal larvae of the two genotypes shows that the "pompon-like" or the "normal-looking" X in male nuclei continues its hyperactive transcription and faster replication as in 24°C reared wild-type larvae. It appears that the hyperactive organization of the hemizygous X in larval male polytene nuclei predisposes its pattern of chromatin condensation to be specifically affected by a variety of genetic, chemical and physical factors. However, the type of chromatin dispersion seen in "pompon-like" X in cold-reared BM2 male larvae does not seem to affect the basic functional (hyperactive) organization of the hemizygous X in male polytene nuclei

AVMf: An Open-Source Framework and Implementation of the Alternating Variable Method

The Alternating Variable Method (AVM) has been shown to be a fast and effective local search technique for search-based software engineering. Recent improvements to the AVM have generalized the representations it can optimize and have provably reduced its running time. However, until now, there has been no general, publicly-available implementation of the AVM incorporating all of these developments. We introduce AVMf, an object-oriented Java framework that provides such an implementation. AVMf is available from http://avmframework.org for configuration and use in a wide variety of projects