arXiv subjects

Y. Segev

Publications and source records attributed to Y. Segev.

5 recordsLinked to original sources

arXiv2026

Composite sub-micron solid particles engineered to enable safe, controllable, efficient, and practical SAI

The properties of candidate particles for solar radiation management (SRM) through stratospheric aerosol injection (SAI) should comply with safety, controllability, and functionality requirements. Following the proposal in arXiv:2604.02283 of safety and controllability requirements, we define here a set of functionality requirements on the particles' properties -- optical properties, stratospheric residence time, scalable manufacturing compatibility, and aerial dispersion compatibility -- that, if met, ensure the feasibility of practical implementation, providing reflection of $\sim1$% of the solar flux. We then present design principles and fabrication methods for sub-micron solid particles that may enable satisfying the combined requirements. These requirements do not identify a unique solution, but favor sub-micron particles with tightly controlled size distributions and stable properties over their stratospheric lifetime, and motivate a composite design where the bulk core composition is selected primarily for optimal radiative properties and the outer shell surface is engineered to control atmospheric chemistry and aging, and enhance aerial dispersion compatibility. We present two specific particle designs that are viable for meeting the coupled requirements: amorphous silica spheres and calcium-carbonate cores surrounded by spherical silica shells (both with appropriate surface treatment). The former is at an advanced stage of experimental verification (described in detail in a companion paper) of meeting all requirements, provides a practical platform for surface engineering, and will enable reaching a substantial fraction of $\sim\!1$% solar flux reflection. The latter is under development and will enable reaching $>1$\% reflection.

physics.ao-ph↗

arXiv2026

A proposal for the safety and controllability requirements that SRM systems should meet

Solar Radiation Modification (SRM) may be the only way to limit global warming in the coming decades, leading to increased interest in the subject and to the expansion of related research & development (R&D) activity. Defining the safety and controllability requirements that any SRM system should meet is crucial for directing R&D activities and enabling governments to make informed decisions on the development and possible implementation of such systems. We present an initial proposal for this set of requirements, which also guides Stardust's R&D, as a basis for further discussion and consideration. While we focus on SRM systems based on Stratospheric Aerosol Injection (SAI), the proposed principles may be applicable more broadly.

physics.ao-ph↗

arXiv2016

Miyamoto involutions in axial algebras of Jordan type half

Nonassociative commutative algebras $A$ generated by idempotents $e$ whose adjoint operators ${\rm ad}_e\colon A \rightarrow A$, given by $x \mapsto xe$, are diagonalizable and have few eigenvalues are of recent interest. When certain fusion (multiplication) rules between the associated eigenspaces are imposed, the structure of these algebras remains rich yet rather rigid. For example vertex operator algebras give rise to such algebras. The connection between the Monster algebra and Monster group extends to many axial algebras which then have interesting groups of automorphisms. Axial algebras of Jordan type $η$ are commutative algebras generated by idempotents whose adjoint operators have a minimal polynomial dividing $(x-1)x(x-η)$, where $η\notin \{0,1\}$ is fixed, with well-defined and restrictive fusion rules. The case of $η\neq \frac{1}{2}$ was thoroughly analyzed by Hall, Rehren, and Shpectorov in a recent paper, in which axial algebras were introduced. Here we focus on the case where $η=\frac{1}{2}$, which is much less understood and is of a different nature.

math.GR↗

arXiv2012

Scanning superconducting quantum interference device on a tip for magnetic imaging of nanoscale phenomena

We describe a new type of scanning probe microscope based on a superconducting quantum interference device (SQUID) that resides on the apex of a sharp tip. The SQUID-on-tip is glued to a quartz tuning fork which allows scanning at a tip-sample separation of a few nm. The magnetic flux sensitivity of the SQUID is 1.8 μ_0/Hz^{1/2} and the spatial resolution is about 200 nm, which can be further improved. This combination of high sensitivity, spatial resolution, bandwidth, and the very close proximity to the sample provides a powerful tool for study of dynamic magnetic phenomena on the nanoscale. The potential of the SQUID-on-tip microscope is demonstrated by imaging of the vortex lattice and of the local AC magnetic response in superconductors.

cond-mat.supr-con↗

arXiv2009

Mott insulator phases and first-order melting in BSCCO crystals with periodic surface holes

We measured the effects of periodic surface holes, created using a focused ion beam, on the phase diagram of the vortex matter in high-T_c Bi_2Sr_2CaCu_2O_{8+δ} crystals. Differential magneto-optical measurements show that the irreversibility line is shifted to higher fields and temperatures, with respect to the pristine melting line. The irreversibility line displays weak field dependence between integer matching fields indicating multiple-flux-quanta pinning at holes. We find reduced equilibrium compressibility of the vortex matter at integer matching fields, which is strong evidence for the existence of thermodynamic Mott insulator phases. Shaking with a transverse ac field surprisingly reveals first-order melting that is not shifted with respect to the pristine melting line and that seems to occur within the Mott insulator regions. This melting is understood to be the first-order transition in the bulk of the crystal beneath the surface holes. The transition is visible at the surface, despite the reduced vortex compressibility in the top layer.

cond-mat.supr-con↗