Integrated Calendar

When we fall asleep, brain function and physiology are rapidly transformed. Understanding the neural basis of sleep requires imaging methods that can capture multiple aspects of brain physiology at fast timescales. We develop approaches for analyzing human brain physiology using multimodal neuroimaging, and apply them to investigate the neural origins and consequences of sleep. We found that accelerated methods for fMRI can enable imaging subsecond neural dynamics throughout the human brain. We applied these methods to investigate the neural dynamics that occur at state transitions, and identified temporal sequences within thalamocortical networks that precede the moment of awakening from sleep. In addition, we developed a method to image cerebrospinal fluid flow, and discovered large waves of fluid flow that appear in the sleeping human brain. Together, these studies highlight the new biological information that can be extracted from fast fMRI data, and use this approach to discover neurophysiological dynamics unique to the sleeping brain.
Link: https://weizmann.zoom.us/j/95406893197?pwd=REt5L1g3SmprMUhrK3dpUDJVeHlrZz09
Meeting ID: 954 0689 3197
Password: 750421

X-ray precision polarimetry and the detection of vacuum birefringence

Vacuum isn’t just empty space. Rather there is a continuous creation and annihilation of virtual pairs. A strong electric field can align them to a certain degree such that vacuum becomes birefringent – according to quantum electrodynamics. The effect has been predicted almost 90 years ago, but never been directly verified to date.

We have been developing X-ray polarimetry over the past 12 years in order to detect vacuum birefringence. The current status is an extinction ratio of 11 orders of magnitude using channel-cut crystals. This is a figure not nearly matched by any other polarimeter in any spectral region. Besides the physics of X-ray polarimetry, I will also discuss the remaining issues for the detection of vacuum birefringence.


The Helium hydride ion in strong laser fields

The Helium hydride ion is considered to be the first molecule that has formed after the big bang, a fact already pointing to the fundamental importance of this ion. Nevertheless, its behavior in intense, ultrashort laser fields has not been addressed until recently. This is in strong contrast to another fundamentally important molecule, the hydrogen molecular ion, on which many thousands of papers have been published.

I will discuss a series of experiments using different isotopologues of the Helium hydride ion at different wavelengths. The dissociation and ionization dynamics turns out to be vastly different from the hydrogen molecular ion. Moreover, it changes dramatically when moving from the near- to the mid-infrared spectral region. Although Helium hydride and the hydrogen molecule are isoelectronic, they can be seen as opposing extremes.

The eIF4E Homolog Protein (4EHP, eIF4E2) is a mRNA cap-binding protein that in contrast to eIF4E cannot interact with eIF4G and acts as a translation repressor. The CCR4-NOT complex functions in miRNA-mediated mRNA silencing through its recruitment by the RISC (RNA-induced silencing complex). The CCR4-NOT complex recruits the helicase DDX6, which binds 4E-T (eIF4E-Transporter), which in turn binds 4EHP resulting in inhibition of cap-dependent translation (Proc. Natl. Acad. Sci. 2017). 4EHP suppresses IFN-production by promoting the miR-34a-induced translational silencing of Ifnb1 mRNA. (Mol. Cell, 2021). The SARS-CoV2 encoded Non-Structural Protein 2 (NSP2), directly interacts with the cellular GIGYF2 protein and enhances the binding of GIGYF2 to 4EHP and thereby enhances translational repression of Ifnb-1 mRNA. Depletion of 4EHP or GIGYF2 resulted in enhanced IFN-ß expression accompanied by a significant reduction of SARS-CoV-2 replication.

For nearly three decades, ultracold atomic gases have been used with great success to study fundamental many-body phenomena such as Bose-Einstein condensation and superfluidity. While traditionally they were produced in harmonic electromagnetic traps and thus had inhomogeneous densities, it is now also possible to create homogeneous samples in the uniform potential of an optical box trap. Box trapping simplifies the interpretation of experimental results, provides more direct connections with theory and, in some cases, allows qualitatively new, hitherto impossible experiments. I will give an overview of our recent experiments with box-trapped three- and two-dimensional Bose gases, focusing on a series of related experiments on non-equilibrium phenomena, including phase-transition dynamics, turbulence, and equilibration of closed quantum systems

Jodi Nunnari is a pioneer in the field of mitochondrial biology. She was the first to describe the organelle as a dynamic network in homeostatic balance and decipher the mechanisms of the machines responsible for mitochondrial division and fusion, which are critical determinants of overall mitochondrial shape and distribution. Nunnari’s laboratory at UC Davis is using system-based approaches to address how mitochondrial behavior is physiologically regulated within cells to shed light onto how mitochondrial dysfunction contributes to human disease.