Configuring the cancellation of optical near-fields

The characteristic near-field behavior of electromagnetic fields is open to a variety of interpretations. In a classical sense the term 'near-field' can be taken to signify a region, sufficiently close to some primary or secondary source, that the onset of retardation features is insignificant; a quantum theoretic explanation might focus more on the large momentum uncertainty that operates at small distances. Together, both near-field and wave-zone (radiative) features are fully accommodated in a retarded resonance propagation tensor, within which each component individually represents one asymptotic limit - alongside a third term that is distinctly operative at distances comparable to the optical wavelength. The propagation tensor takes different forms according to the level of multipole involved in the signal production and detection. In this presentation the nature and symmetry properties of the retarded propagation tensor are explored with reference to various forms of electric interaction, and it is shown how a suitable arrangement of optical beams can lead to the complete cancellation of near-fields. The conditions for such behavior are fully determined and some important optical trapping applications are discussed

Optically induced multi-particle structures: multi-dimensional energy landscapes

Recent quantum electrodynamical studies on optically induced inter-particle potential energy surfaces have revealed unexpected features of considerable intricacy. The exploitation of these features presents a host of opportunities for the optical fabrication of nanoscale structures, based on the fine control of a variety of attractive and repulsive forces, and the torques that operate on particle pairs. Here we report an extension of these studies, exploring the first detailed potential energy surfaces for a system of three particles irradiated by a polarized laser beam. Such a system is the key prototype for developing generic models of multi-particle complexity. The analysis identifies and characterizes potential points of stability, as well as forces and torques that particles experience as a consequence of the electromagnetic fields, generated by optical perturbations. Promising results are exhibited for the optical fabrication of assemblies of molecules, nanoparticles, microparticles, and colloidal multi-particle arrays. The comprehension of mechanism that is emerging should help determine the fine principles of multi-particle optical assembly

Multiheterodyne Detection and Sampling of Periodically Filtered White Light for Correlations at 20 km of Delay

A frequency comb is used as a set of coherent local oscillators to downconvert and spectrally compress white light that has been periodically filtered by a Fabry-Perot etalon. Multiheterodyne detection allows white light spread across 100 GHz of optical spectrum to be compressed to 5 GHz of radio frequency (RF) bandwidth for electronic sampling on an oscilloscope. Correlations are observed at delays of up to 20 km with a minimum resolution of less than 1 mm. Calculations show that resolution may be easily increased by increasing etalon finesse and frequency comb bandwidth

Carbon dioxide system in the Canary region during October 1995

During the cruise F/S Poseidon 212/3 (September 30-October 8, 1995) determination of carbon system variables was carried out over the section of La Palma-La Graciosa and at the ESTOC station in the Canary Island area. Total alkalinity and pH in the total scale at 25 degreesC were determined at 24 stations from surface to bottom. In this area, the presence of different water masses can be traced by the carbon system variables. NACW is defined by a strong gradient of A(T) and pH from 150 to 750 m. MW is characterised by high values of A(T) and pH between 1000 to 1200 in and AAIW signals are found at around 900 in in the strait between Gran Canaria and Fuerteventura with low A(T), low pH and a maximum of fCO(2). Assuming an atmospheric mean value of fCO(2) of 360 mu atm and an average surface value of 393 +/-7 mu atm, we can conclude that during this cruise this oceanic area tends to release CO2 into the atmosphere, acting as a weak source with a carbon flux towards the atmosphere of +8.0 +/-1.8 mmol.m(-2)d(-1). The saturation levels in the Canary Island area have been found to be higher than 3600 m for calcite and 2700 in for aragonite. The inorganic carbon/organic carbon ratio (IC/OC) varies from 0.07 at 300 m to 0.5 at 3000 m. The IC/OC ratio shows that about a 34% increase in the C-T of the deep water is contributed by the inorganic CaCO3 dissolution. The IC at 300 in is around 7 mu mol kg(-1), increasing with depth to 37.5 mu mol kg(-1) at 3700 m

Measurement of carrier envelope offset frequency for a 10 GHz etalon-stabilized semiconductor optical frequency comb

We report Carrier Envelope Offset (CEO) frequency measurements of a 10 GHz harmonically mode-locked, Fabry-Perot etalon-stabilized, semiconductor optical frequency comb source. A modified multi-heterodyne mixing technique with a reference frequency comb was utilized for the measurement. Also, preliminary results from an attempt at f-2f self-referencing measurement are presented. The CEO frequency was found to be similar to 1.47 GHz for the particular etalon that was used

Electrosprayed Minocycline-loaded PLGA Microparticles for the Treatment of Glioblastoma

Background: Around 12,340 patients in the US are diagnosed with glioblastoma multiforme (GBM) yearly, and despite the current treatment options, such as chemotherapy, radiotherapy, surgical resection, or a combination of them, the median survival is only about 15 months after initial diagnosis. Minocycline, a tetracycline antibiotic, has shown to inhibit U87 glioblastoma cell death and inhibit angiogenesis, or the creation of new blood vessels as is often needed by the tumor to grow. The utilization of biomaterials such as poly lactic-co-glycolic acid (PLGA) can better sustain the release and bioactivity of loaded drugs. The use of polyethylene glycol (PEG), a hydrophilic polymer, may improve the encapsulation of minocycline into the PLGA microparticles, given its hydrophilic nature. Electrospraying may be a promising method to fabricate drug loaded PLGA microparticles with high drug loading and loading efficiency. Therefore, the objective of this project was to develop electrosprayed minocycline-loaded PLGA microparticles for the treatment of GBM. Methods: Minocycline-loaded PLGA microparticles were fabricated through electrospraying utilizing an 18 cm needle-tip to glass plate distance, 0.9 ml/hr flowrate, and 14 kV voltage. The solution consisted of 1 ml of chloroform as the solvent and 70 mg of PLGA as the polymer with different minocycline amounts and with or without polyethylene glycol (PEG). The amount of drug loaded into the microparticles was determined by dissolving the microparticles in 1 mL of dimethylsulfoxide and then measuring the absorbance of minocycline at 350 nm. Release kinetics studies were performed by placing the microparticles in phosphate-buffered saline and reading minocycline absorbance of the supernatant at various timepoint. Scanning Electron Microscopy (SEM) was used to determine size and morphology of the minocycline-loaded PLGA microparticles. Results: The amount of drug loading and loading efficiency increased with the addition of PEG (3.23 ± 0.29 vs. 4.02 ± 0.34 and 49.40 ± 4.49 vs. 64.30 ± 5.47%, respectively) and the utilization of higher amount of drug (4.02 ± 0.34 vs. 9.93 ± 0.64 and 64.30 ± 5.47 vs. 70.76 ± 4.57%, respectively). The release kinetics study demonstrated that the different microparticles experienced a burst release within the first hour (67-80%). The microparticles were spherical in shape and ranged between 4-11 μm in size. The addition of PEG resulted in the aggregation of the microparticles, as observed in SEM imaging. Conclusions: This study demonstrated that electrosprayed minocycline-loaded PLGA microparticles can be successfully fabricated with high drug loading and loading efficiency and have a spherical shape within the micron size range. PEG was able to increase drug loading of the lipophilic drug by increasing the solubility of the drug in the polymer/chloroform solution. However, the utilization of PEG affected the collection of the particles and therefore, further optimization of the electrospraying parameters needs to be done to improve the collection of non-aggregated microparticles. In addition, given their burst release of minocycline, the microparticles may need to be further encapsulated in a scaffold or depot to prolong their release of drug

Optimizing the linearity in high-speed photodiodes

Analog photonic links require high-fidelity, high-speed optical-to-electrical conversion for applications such as radio-over-fiber, synchronization at kilometer-scale facilities, and low-noise electronic signal generation. Photodetector nonlinearity is a particularly vexing problem, causing signal distortion and excess noise, especially in systems utilizing ultrashort optical pulses. Here we show that photodetectors designed for high power handling and high linearity can perform optical-to-electrical conversion of ultrashort optical pulses with unprecedented linearity over a large photocurrent range. We also show that the broadband, complex impedance of the circuit following the photodiode modifies the linearity significantly. By externally manipulating the circuit impedance, we extend the detector's linear range to higher photocurrents, with over 50 dB rejection of amplitude-to-phase conversion for photocurrents up to 40 mA. This represents a 1000-fold improvement over state-of-the-art photodiodes and significantly extends the attainable microwave power by a factor of four. As such, we eliminate the long-standing requirement in ultrashort pulse detection of precise tuning of the photodiode's operating parameters (average photocurrent, bias voltage or temperature) to coincide with a nonlinearity minimum. These results should also apply more generally to reduce nonlinear distortion in a range of other microwave photonics applications

Impaired AMPA signaling and cytoskeletal alterations induce early synaptic dysfunction in a mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is a devastating neurodegenerative disorder that impairs memory and causes cognitive and psychiatric deficits. New evidences indicate that AD is conceptualized as a disease of synaptic failure, although the molecular and cellular mechanisms underlying these defects remain to be elucidated. Determining the timing and nature of the early synaptic deficits is critical for understanding the progression of the disease and for identifying effective targets for therapeutic intervention. Using single-synapse functional and morphological analyses, we find that AMPA signaling, which mediates fast glutamatergic synaptic transmission in the central nervous system (CNS), is compromised early in the disease course in an AD mouse model. The decline in AMPA signaling is associated with changes in actin cytoskeleton integrity, which alters the number and the structure of dendritic spines. AMPA dysfunction and spine alteration correlate with the presence of soluble but not insoluble Aβ and tau species. In particular, we demonstrate that these synaptic impairments can be mitigated by Aβ immunotherapy. Together, our data suggest that alterations in AMPA signaling and cytoskeletal processes occur early in AD. Most important, these deficits are prevented by Aβ immunotherapy, suggesting that existing therapies, if administered earlier, could confer functional benefits