Engineering terahertz surface magnon-polaritons in hyperbolic antiferromagnets

Magnetic crystals were recently studied as a route to hyperbolic dispersion and the effects associated with it. These studies, however, concentrated on bulk waves and frequencies where transmission is possible and where negative refraction occurs. Here, in contrast, we concentrate on geometries which sample regions of the dispersion relations where bulk propagation is not possible. This is done by controlling the orientation of the uniaxial anisotropy axis with respect to the surface of the crystal. Furthermore, we find that new magnetic surface polaritons exist in these regions, and we investigate the nature of these waves. In addition, significant tunability can be introduced by applying an external field perpendicular to the easy axes of a uniaxial antiferromagnet, creating a canted structure and generally shifting the frequencies to higher values. This externally applied field dramatically changes the nature of both surface and bulk polaritons, making them highly nonreciprocal

Oriented asymmetric wave propagation and refraction bending in hyperbolic media

Crystal quartz is a well-known anisotropic medium with optically active phonons in the THz region where hyperbolic phonon-polaritons can be excited. Here, we use this material to illustrate how the behavior of bulk and surface hyperbolic polaritons can be drastically modified by changing the orientation of the crystal’s anisotropy axis with respect to its surface. We demonstrate, both theoretically and experimentally, phenomena associated with the orientation of hyperbolic media. We show the consequences of changes in the crystal’s orientation in various ways, such as the modification of the effective reststrahl regions and associated surface phonon polariton dispersion. Of particular significance, however, is the transmission behavior of radiation passing through a rotated hyperbolic crystal. Here, even a small rotation of the optical axes with respect to the crystal surface can lead to a very large degree of asymmetry in the transmitted intensity. In addition, the refracting angle (which in a hyperbolic medium may correspond to negative refraction and slab lensing behavior) itself becomes asymmetric, so that a slab lens with a laterally displaced image becomes possible. We discuss some of the possible consequences of these types of effects

Using magnetic hyperbolic metamaterials as high frequency tunable filters

Metamaterials have enabled a series of major advances in optical devices in the past decade. Here, we suggest a type of hyperbolic metamaterial based on spin canting in magnetic multi-layers. We show that these structures have unique features in microwave waveguides that act as tunable filters. In the resulting band pass filter, we demonstrate an exceptional frequency tunability of 30 GHz with external fields smaller than 500 Oe. Unlike single metallic ferromagnetic films, we also demonstrate a high-frequency band-stop filter at very low fields

Nonreciprocity in millimeter wave devices using a magnetic grating metamaterial

The control and manipulation of many of light's fundamental properties, such as reflectivity, has become a topic of increasing interest since the advent of engineered electromagnetic structures—now known as metamaterials. Many of these metamaterial structures are based on the properties of dielectric materials. Magnetic materials, on the other hand, have long been known to interact with electromagnetic waves in unusual ways; in particular, their nonreciprocal properties have enabled rapid advances in millimeter wave technology. Here, we show how a structured magnetic grating can be employed to engineer electromagnetic response at frequencies upwards of hundreds of gigahertz. In particular, we investigate how nonreciprocal reflection can be induced and controlled in this spectral region through the composition of the magnetic grating. Moreover, we find that both surface and guided polaritons contribute to high-frequency nonreciprocity; the nature of these is also investigated. Control of electromagnetic radiation at high frequencies is a current challenge of communications technology where our magnetic gradient might be employed in devices including signal processing filters and unidirectional isolators

Cellular metabolism as a basis for immune privilege

We hypothesize that the energy strategy of a cell is a key factor for determining how, or if, the immune system interacts with that cell. Cells have a limited number of metabolic states, in part, depending on the type of fuels the cell consumes. Cellular fuels include glucose (carbohydrates), lipids (fats), and proteins. We propose that the cell's ability to switch to, and efficiently use, fat for fuel confers immune privilege. Additionally, because uncoupling proteins are involved in the fat burning process and reportedly in protection from free radicals, we hypothesize that uncoupling proteins play an important role in immune privilege. Thus, changes in metabolism (caused by oxidative stresses, fuel availability, age, hormones, radiation, or drugs) will dictate and initiate changes in immune recognition and in the nature of the immune response. This has profound implications for controlling the symptoms of autoimmune diseases, for preventing graft rejection, and for targeting tumor cells for destruction

The effects of chemotherapeutics on cellular metabolism and consequent immune recognition

A widely held view is that oncolytic agents induce death of tumor cells directly. In this report we review and discuss the apoptosis-inducing effects of chemotherapeutics, the effects of chemotherapeutics on metabolic function, and the consequent effects of metabolic function on immune recognition. Finally, we propose that effective chemotherapeutic and/or apoptosis-inducing agents, at concentrations that can be achieved physiologically, do not kill tumor cells directly. Rather, we suggest that effective oncolytic agents sensitize immunologically altered tumor cells to immune recognition and immune-directed cell death

Emergent dynamic chirality in a thermally driven artificial spin ratchet

Modern nanofabrication techniques have opened the possibility to create novel functional materials, whose properties transcend those of their constituent elements. In particular, tuning the magnetostatic interactions in geometrically frustrated arrangements of nanoelements called artificial spin ice1, 2 can lead to specific collective behaviour3, including emergent magnetic monopoles4, 5, charge screening6, 7 and transport8, 9, as well as magnonic response10, 11, 12. Here, we demonstrate a spin-ice-based active material in which energy is converted into unidirectional dynamics. Using X-ray photoemission electron microscopy we show that the collective rotation of the average magnetization proceeds in a unique sense during thermal relaxation. Our simulations demonstrate that this emergent chiral behaviour is driven by the topology of the magnetostatic field at the edges of the nanomagnet array, resulting in an asymmetric energy landscape. In addition, a bias field can be used to modify the sense of rotation of the average magnetization. This opens the possibility of implementing a magnetic Brownian ratchet13, 14, which may find applications in novel nanoscale devices, such as magnetic nanomotors, actuators, sensors or memory cells

Exploring Projections for HIV Infection with Pre-Exposure Prophylaxis Usage in a High-Risk Population

Prevention of type-1 human immunodeficiency virus (HIV) infections has primarily been through condom usage, abstinence, and behavioral and risk awareness programs. Pre-exposure prophylaxis (PrEP) medications became approved for infection prevention in 2012. Mathematical models exploring the projections and impacts of PrEP on the spread of HIV are sparse. This study develops an epidemiological model for type-1 HIV infection accounting for both PrEP and condom usage. We utilized CDC surveillance data on HIV/AIDS statistics to develop a susceptible, infected, AIDS numerical model containing PrEP, condoms, and the combination of both. We explore projections with the percentages of PrEP usage held constant and the impact of average annual sexual partners. We find when 70% of the high-risk population uses PrEP properly with an average of 2 sexual partners per year, the eventual infected percentage drops to about 15%. In contrast, when PrEP is not used correctly and with 4 partners per year the total eventual infected percentage rises to 59%. PrEP can be a highly effective mitigator for the spread of HIV. However, an increased average number of sexual partners per year with improper PrEP usage can minimize the long-term effectiveness of PrEP

Exploring Projections for HIV Infection with Pre-Exposure Prophylaxis Usage in a High-Risk Population

Prevention of type-1 human immunodeficiency virus (HIV) infections has primarily been through condom usage, abstinence, and behavioral and risk awareness programs. Pre-exposure prophylaxis (PrEP) medications became approved for infection prevention in 2012. Mathematical models exploring the projections and impacts of PrEP on the spread of HIV are sparse. This study develops an epidemiological model for type-1 HIV infection accounting for both PrEP and condom usage. We utilized CDC surveillance data on HIV/AIDS statistics to develop a susceptible, infected, AIDS numerical model containing PrEP, condoms, and the combination of both. We explore projections with the percentages of PrEP usage held constant and the impact of average annual sexual partners. We find when 70% of the high-risk population uses PrEP properly with an average of 2 sexual partners per year, the eventual infected percentage drops to about 15%. In contrast, when PrEP is not used correctly and with 4 partners per year the total eventual infected percentage rises to 59%. PrEP can be a highly effective mitigator for the spread of HIV. However, an increased average number of sexual partners per year with improper PrEP usage can minimize the long-term effectiveness of PrEP