לוח שנה משולב

The general synchronization problem asks to recover states of objects from their corrupted relative measurements. When the states are represented by group elements (e.g. 3-D rotations or permutations) this problem is known as group synchronization. In several applications, the algebraic structure of the states is more complicated, for example, the states can be represented by partial permutations. The synchronization problem has many applications, in particular, to structure-from-motion (SfM), where one needs to estimate the 3D structure of a scene from a set of its projected 2D images. I will first describe a general framework for group synchronization, the Cycle-Edge Message Passing (CEMP), and then explain its generalization to non groups, by exemplifying the case of partial permutation synchronization. I will emphasize mathematical difficulties, review some mathematical guarantees for the proposed methods and also demonstrate an application. This is a joint work with Shaohan Li and Yunpeng Shi.

Mantle fluids are the primary carriers of key volatile elements that make the Earth’s long-term planetary habitability possible. The interaction of such volatile-rich fluids with the mantle rocks, especially the sub-cratonic lithospheric mantle leads to alteration of the mantle as well as its melting. High-density fluids encased inside diamonds are the best natural representation of mantle fluid compositions, suggesting their compositions are saline, silicic or carbonatitic. However, the origin and role in the mantle as well as their role in altering the mantle are still unclear.
In my research, we approach these questions by experimentally simulating the interaction of volatile-rich fluids with mantle rocks at known pressure and temperature relevant to the mantle. Examining different mixtures of volatiles (H2O and CO2) and mantle rocks (peridotite and eclogite), we attempt to understand the origin of each type of fluid found in diamonds as well as study the effect of such interaction on the mantle chemistry and mineralogy.
Compiling many experimental studies reveals that fluids ranging from silicic to low-Mg carbonatitic are formed in systems of eclogite+H2O+CO2, the more CO2 in the system, the more carbonatitic the fluid is. Fluids ranging from low-Mg carbonatitic to high-Mg carbonatitic in nature are the results of the formation of fluids in the peridotite-H2O-CO2 system. The more CO2 in the system, the more high-Mg carbonatitic the fluid composition is. These results suggest that the various fluids found in the mantle result from changes in the bulk composition of the mantle rocks.
The mantle rocks are significantly affected during percolation of such fluids through them. For example, experimentally interacting silicic fluid with peridotite demonstrated the formation of various metasomatic peridotites as a function of pressure and temperature, composing of amphibole and mica. The mineral assemblages, chemistry, and P-T conditions in the experiments are similar to those found in metasomatic xenoliths from Kimberly, South Africa, and surrounding localities.

Solar panels are well known to produce electricity, but they are also in early-stage development for the production of sustainable fuels and chemicals. These panels mimic plant leaves in shape and function as demonstrated for overall solar water splitting to produce green H2 by the laboratories of Nocera and Domen.1,2
This presentation will give an overview of our recent progress to construct prototype solar panel devices for the conversion of carbon dioxide and solid waste streams into fuels and higher-value chemicals through molecular surface-engineering of solar panels with suitable catalysts. Specifically, a standalone ‘photoelectrochemical leaf’ based on an integrated lead halide perovskite-BiVO4 tandem light absorber architecture has been built for the solar CO2 reduction to produce syngas.3 Syngas is an energy-rich gas mixture containing CO and H2 and currently produced from fossil fuels. The renewable production of syngas may allow for the synthesis of renewable liquid oxygenates and hydrocarbon fuels. Recent advances in the manufacturing have enabled the reduction of material requirements to fabricate such devices and make the leaves sufficiently light weight to even float on water, thereby enabling application on open water sources.4 The tandem design also allows for the integration of biocatalysts and the selective and bias-free conversion of CO2-to-formate has been demonstrated using enzymes.5 The versatility of the integrated leaf architecture has been demonstrated by replacing the perovskite light absorber by BiOI for solar water and CO2 splitting to demonstrate week-long stability.6
An alternative solar carbon capture and utilisation technology is based on co-deposited semiconductor powders on a conducting substrate.2 Modification of these immobilized powders with a molecular catalyst provides us with a photocatalyst sheet that can cleanly produce formic acid from aqueous CO2.7 CO2-fixing bacteria grown on such a ‘photocatalyst sheet’ enable the production of multicarbon products through clean CO2-to-acetate conversion.8 The deposition of a single semiconductor material on glass gives panels for the sunlight-powered conversion plastic and biomass waste into H2 and organic products, thereby allowing for simultaneous waste remediation and fuel production.9 The concept and prospect behind these integrated systems for solar energy conversion,10 related approaches,11 and their relevance to secure and harness sustainable energy supplies in a fossil-fuel free economy will be discussed.