Superpositions of up to six plane waves without electric-field interference

Superpositions of coherent light waves typically interfere. We present superpositions of up to six plane waves that defy this expectation by having a perfectly homogeneous mean square of the electric field. For many applications in optics, these superpositions can be seen as having a homogeneous intensity. Our superpositions show interesting one-, two-, and three-dimensional patterns in their helicity densities, including several that support bright regions of superchirality. Our superpositions might be used to write chiral patterns in certain materials, and, conversely, such materials might be used as the basis of an “optical helicity camera” capable of recording spatial variations in helicity

Radiative spin polarization in an ultrastrong magnetic field

We calculate the spin flip rates for an electron in a homogeneous magnetic field for low excitations ($N\le 5$). Our results apply for all field strengths including those beyond the critical field strength at which the spin contributes as much to the electron's energy as its rest mass. Existing approximations either assume that the electron is in a sufficiently highly excited state such that its orbit can be assumed to be classical or the magnetic field be weak compared to the critical field. The regime of high magnetic field strength and low excitations is therefore poorly covered by them. By comparing our calculations to different approximations, we find that in the high field, low excitation regime the spin flip rates are lower and the equilibrium spin polarization is less pure then one would get by naively applying existing approximations in this regime.Comment: 9 pages, 6 figure

Nonuniform currents and spins of relativistic electron vortices in a magnetic field

We present a relativistic description of electron vortex beams in a homogeneous magnetic field. Including spin from the beginning reveals that spin-polarized electron vortex beams have a complicated azimuthal current structure, containing small rings of counterrotating current between rings of stronger corotating current. Contrary to many other problems in relativistic quantum mechanics, there exists a set of vortex beams with exactly zero spin-orbit mixing in the highly relativistic and nonparaxial regime. The well defined phase structure of these beams is analogous to simpler scalar vortex beams, owing to the protection by the Zeeman effect. For states that do show spin-orbit mixing, the spin polarization across the beam is nonuniform rendering the spin and orbital degrees of freedom inherently inseparable.Comment: 5 pages + supplemental materia

Antiviral agents in hepatitis B virus transfected cell lines: Inhibitory and cytotoxic effect related to time of treatment

The antiviral and cytotoxic effects of ara-arabinoside monophosphate, 2′,3′, dideoxy-cytidine, ganciclovir, 9-2(-phosphonylmethoxyethyl) adenine, 2′,3′-dideoxy-3′-thiacytidine and recombinant interferon-alpha were studied using two human hepatitis B virus transfected hepatoma cell lines, HepG2 2.2.15 and HB 611. After 9 days of exposure, starting on day 3 after seeding, inhibition of extracellular HBV-DNA expressed as ID50 was in the 0.1–1.0 μM range for 2′,3′-dideoxy-3′-thiacytidine and 9-2(-phosphonylmethoxyethyl) adenine and >10 μM for dideoxy-cytidine, ara-arabinoside monophosphate and ganciclovir in both cell lines. At 2.500 U/ml recombinant interferon-alpha showed less than 20% inhibition in both cell lines. The HBV-DNA inhibitory effects of 2′,3′-dideoxy-3′-thiacytidine and 9-2(-phosphonylmethoxyethyl) adenine were also investigated after 1 and 3 days of exposure. In t

Spin and helicity in structured waves for light and electrons

This dissertation consists of two parts, connected by the overarching theme of the dynamics of structured waves with internal degrees of freedom. Part I concerns light, whose internal degree of freedom is polarisation. We investigate the helicity, or handedness of light, which is a good quantum number for massless fields in general and light in particular. In free space it is always possible to describe the light field in a basis left- and right handed helicity modes which are solutions of Maxwell's equations, regardless what spatial structure is chosen. This is useful for bases of highly inhomogeneous waves, such as Bessel waves, for which the spin cannot be unambiguously defined. In chapter 1 we study the conservation of helicity and the preservation of its underlying symmetry, electric-magnetic duality symmetry when light travels through inhomogeneous and/or anisotropic media. We will discuss some of the unique properties of duality symmetric media and reformulate Maxwell's equations in such a way that the decoupling of different helicities for duality symmetric media becomes apparent. The feasibility of constructing duality symmetric media is discussed at the end of the chapter. In chapter 2 we consider superpositions of plane electromagnetic waves in free space. Such superpositions typically interfere. We present superpositions of up to six plane waves which defy this expectation by having a perfectly homogeneous mean square of the electric field. Because most matter interacts much stronger with the electric than with the magnetic field, these superpositions can be considered noninterfering. Our superpositions show complex patterns in their helicity densities, of which we will show many examples. We study the effects on our helicity patterns of imperfections that may occur in a realistic experiment: deviations from the optimal amplitudes, phases and polarisations of the superposed waves, small misalignments and partially coherent light. Our superpositions can be used to write chiral patterns in light sensitive liquid crystals. Conversely, these liquid crystals can be used for an `optical helicity camera' which records spatial variations in helicity. In the final paragraph of chapter 2 we discuss some mathematical questions concerning noninterfering superpositions. Part II concerns electrons, whose internal degree of freedom is spin. In chapter 3 we will present analytical solutions of the Dirac equation for an electron vortex beam in a homogeneous magnetic field. Including spin from the beginning reveals that spin polarised electron vortex beams have a complicated azimuthal current structure, containing small rings of counterrotating current between rings of stronger corotating current. Contrary to many other problems in relativistic quantum mechanics, there exist vortex beam solutions with exactly zero spin-orbit mixing in the highly relativistic and nonparaxial regime. Chapter 4 treats the interaction between electron vortex states in a homogeneous magnetic field and light, where we expand and quantise the radiation field in a basis of Bessel modes with definite helicity. Our results apply for magnetic field strength beyond the critical field strength at which the spin contributes as much to the electron's energy as its rest mass. We are able to compute spin flip rates for low lying states, finding a much higher degree of equilibrium spin polarisation than approximations for high lying electron states suggested

Biomolecular therapies for chronic discogenic low back pain: A narrative review

Chronic low back pain caused by intervertebral disc (IVD) degeneration, also termed chronic discogenic low back pain (CD-LBP), is one of the most prevalent musculoskeletal diseases. Degenerative processes in the IVD, such as inflammation and extra-cellular matrix breakdown, result in neurotrophin release. Local elevated neurotrophin levels will stimulate sprouting and innervation of sensory neurons. Furthermore, sprouted sensory nerves that are directly connected to adjacent dorsal root ganglia have shown to increase microglia activation, contributing to the maintenance and chronification of pain. Current pain treatments have shown to be insufficient or inadequate for long-term usage. Furthermore, most therapeutic approaches aimed to target the underlying pathogenesis of disc degeneration focus on repair and regeneration and neglect chronic pain. How biomolecular therapies influence the degenerative IVD environment, pain signaling cascades, and innervation and excitability of the sensory neurons often remains unclear. This review addresses the relatively underexplored area of chronic pain treatment for CD-LBP and summarizes effects of therapies aimed for CD-LBP with special emphasis on chronic pain. Approaches based on blocking pro-inflammatory mediators or neurotrophin activity have been shown to hamper neuronal ingrowth into the disc. Furthermore, the tissue regenerative and neuro inhibitory properties of extracellular matrix components or transplanted mesenchymal stem cells are potentially interesting biomolecular approaches to not only block IVD degeneration but also impede pain sensitization. At present, most biomolecular therapies are based on acute IVD degeneration models and thus do not reflect the real clinical chronic pain situation in CD-LBP patients. Future studies should aim at investigating the effects of therapeutic interventions applied in chronic degenerated discs containing established sensory nerve ingrowth. The in-depth understanding of the ramifications from biomolecular therapies on pain (chronification) pathways and pain relief in CD-LBP could help narrow the gap between the pre-clinical bench and clinical bedside for novel CD-LBP therapeutics and optimize pain treatment

Beleving van water in de stad: een literatuurstudie

Mensen wonen en werken bij water in de stad en willen ook steeds meer betrokken raken bij het waterbeheer in de stad. Uit onderzoek blijkt dat een leefomgeving, die plezierig overkomt op mensen, leidt tot sterke tevredenheid en geluk. Die positieve beleving van burgers draagt bij tot meer acceptatie, medewerking en begrip bij ingrepen in en aanpassingen van het watersysteem. Het is daarom belangrijk om na te gaan hoe water door de burger wordt beleefd en dit mee te nemen in het ontwerp van watersystemen. Land en water zijn allebei bepalend voor de kwaliteit van het landschap en moeten op elkaar worden afgestemd. Het water moet passen in het beeld dat mensen van de omgeving hebbe