Control of atom-photon interactions with shaped quantum electron wavepackets

Photon emission from atoms and free electrons underlie a wealth of fundamental science and technological innovations. We present a regime where atom-photon and electron-photon interactions interfere with each other, resulting in substantial changes in the spontaneous emission rate compared to the sum of each interaction considered in isolation. We highlight the critical role played by quantum electron wavepackets, and how the emission can be tailored via the electron waveshape, as well as the atomic population and coherence. Our findings reveal that atom-photon and electron-photon interactions cannot be considered in isolation even when higher-order contributions involving all three bodies (atom, photon and free electron) are negligible. Our findings pave the way to more precise control over photon emission processes and related diagnostics.Comment: 9 pages, 4 figure

Broadband strong optical dichroism in topological Dirac semimetals with Fermi velocity anisotropy

Prototypical three-dimensional (3D) topological Dirac semimetals (DSMs), such as Cd$_3$As$_2$ and Na$_3$Bi, contain electrons that obey a linear momentum-energy dispersion with different Fermi velocities along the three orthogonal momentum dimensions. Despite being extensively studied in recent years, the inherent \emph{Fermi velocity anisotropy} has often been neglected in the theoretical and numerical studies of 3D DSMs. Although this omission does not qualitatively alter the physics of light-driven massless quasiparticles in 3D DSMs, it does \emph{quantitatively} change the optical coefficients which can lead to nontrivial implications in terms of nanophotonics and plasmonics applications. Here we study the linear optical response of 3D DSMs for general Fermi velocity values along each direction. Although the signature conductivity-frequency scaling, $\sigma(\omega) \propto \omega$, of 3D Dirac fermion is well-protected from Fermi velocity anisotropy, the linear optical response exhibits strong linear dichroism as captured by the \emph{universal} extinction ratio scaling law, $\Lambda_{ij} = (v_i/v_j)^2$ (where $i\neq j$ denotes the three spatial coordinates $x,y,z$, and $v_i$ is the $i$-direction Fermi velocity), which is independent of frequency, temperature, doping, and carrier scattering lifetime. For Cd$_3$As$_2$ and Na$_3$Bi$_3$, an exceptionally strong extinction ratio larger than 15 and covering broad terahertz window is revealed. Our findings shed new light on the role of Fermi velocity anisotropy in the optical response of Dirac semimetals and open up novel polarization-sensitive functionalities, such as photodetection and light modulation.Comment: 8 pages, 3 figure

Preliminary Trials on juvenile Macrobrachium rosenbergii Production under modified Static 'Green water' Conditions

The methods of juvenile production of Udang Galah (Macrobrachium rosenbergii) have been documented by several workers (ling, 1969 .. Ling and Costello, 1976 .. Fujimura 7966, 1967, 1968, 1972 .. Fujimura and okomoto, 1970,. Sandifer etl.1976). The methods given by these workers involve intensive hatchery management such as frequent water change and cleaning of larval tanks to ensure good sanitation. Such a technique would involve wastage of sea water and at the same time is labour intensive. 'to overcome the above mentioned problems a study 'was conducted at the hatchery of the Faculty of Fisheries and marine Science, Serdang, to produce" Udang Galah" juveniles 'Without water change and by using «green water' at salinities 6~8°100 and 12-14% 0 respectively. Previous studies by Cohen et al. (1976) have conclusively shozon that (green water' is an efficient system to remove toxic metabolites such as ammonia from the culture medium. The 'green water' 'which mainly consists of unicellular algae such as Chlorella is produced by expos;'lg 'loater of salim'ty 6°(00 'Which contained Sarothcrodon mossambicus to sunlight (Fujimura

Selection of broodstock of Tiger Prawn, penaeus monodon fabricius, on the basis of Morphometric traits

Mature Penaeus monodon were collected from Kedah, Perak, Terengganu, johore and Sabah waters in Malaysia. Selected morphometric characters and body weight Were measured individually. The results showed that the females were significantly larger (P<O.05) than the males in all locations. Stepwise regression analysis indicated that carapace length alone is sufficient to explain the variance in body weight for male and female prawns and can thus be used as a criterion for the selection of broadstock. The logarithmic relationships between body weight and total length. body weight and carapace length, and between carapace length and total length for both sexes were also calculated

Ingestion efficiency of Macrobrachium rosenbergii (de Man) larvae feeding on Artemia, Moina micrura Kurz and their combination

Ingestion efficiency of Macrobrachium rosenbergii (de Man) larvae feeding on Artemia alone (A), Moina alone (M) and a 50:50 mixture of Artemia and Moina (AM) at 1, 3, 5 and 7 organisms ml-1 densities was investigated in terms of individual ingestion rate (IIR), dry mass ingestion (DMI) and energy intake (EI). Irrespective of larval stages and test food densities, larvae showed a significantly higher IIR for diet A except for AM, as the IIR for A and AM were similar from stage V onwards. Compared with diet A, IIR of M were sevenfold to fourfold lower, up to stage V. However, the larvae showed a sharp increase in IIR thereafter and gradually the differences reduced to about 1.6-1.2 fold at later stages. Despite the lower IIR, both DMI and EI for Moina were higher from stage VIII onwards than values for Artemia. In case of mixed diet (AM), the larvae of all stages showed a food selectivity response

Efficient generation of extreme terahertz harmonics in 3D Dirac semimetals

Frequency multiplication of terahertz signals on a solid state platform is highly sought-after for the next generation of high-speed electronics and the creation of frequency combs. Solutions to efficiently generate extreme harmonics (up to the $31^{\rm{st}}$ harmonic and beyond) of a terahertz signal with modest input intensities, however, remain elusive. Using fully nonperturbative simulations and complementary analytical theory, we show that 3D Dirac semimetals (DSMs) have enormous potential as compact sources of extreme terahertz harmonics, achieving energy conversion efficiencies beyond $10^{-5}$ at the $31^{\rm{st}}$ harmonic with input intensities on the order of $10$ MW/cm$^2$, over $10^5$ times lower than in conventional THz high harmonic generation systems. Our theory also reveals a fundamental feature in the nonlinear optics of 3D DSMs: a distinctive regime where higher-order optical nonlinearity vanishes, arising as a direct result of the extra dimensionality in 3D DSMs compared to 2D DSMs. Our findings should pave the way to the development of efficient platforms for high-frequency terahertz light sources and optoelectronics based on 3D DSMs.Comment: 10 pages, 3 figure

Least-Cost Feed Formulation for Juvenile Macrobrachium rosenbergii (De Man) by Using the Linear Programming Technique

Linear least-cost programming was used in juvenile M. rosenbergii feed formulation using locally available feed ingredients (fish meal, shrimp meal, copra meal, soybean meal, wheat flour and palm oil). The following constraints were established: the essential amino acid contents were closely similar to those of juvenile M. rosenbergii, crude fat 5-10% and gross energy 4,400 cal/g with least cost. Four types offeed were produced with protein ranges from 25% to 50%. Growth responses of juvenile M. rosenbergii fed these formulated feeds showed that the 40% protein feed (P40) supported the best specific growth rate and feed conversion ratio. P40 feed is recommended for juvenile M. rosenbergii