Transverse susceptibility of nickel thin films with uniaxial anisotropy.

A finite temperature Stoner-Wohlfarth model has been used to calculate the transverse susceptibility of an ensemble of ferromagnetic particles with distributed anisotropy. The simulated transverse susceptibility is in excellent agreement with data acquired from thin film samples of elemental nickel, deposited on 128° Y-cut LiNb03. A strong, well-defined, uniaxial anisotropy is induced in the nickel film by low temperature annealing. Three peaks in the transverse susceptibility are observed in both the measured and simulated data when the applied field is misaligned with the hard axis by a few degrees. Two broad, reversible peaks occur when the applied field is equal to the anisotropy field. A single, sharp irreversible peak occurs when the absolute value of the applied field is less than the anisotropy field, and is associated with a metastable magnetic state. The irreversible peak disappears when the applied field is well aligned with the hard axis. The observed transverse susceptibility is consistent with the theoretical predictions of Aharoni et al. and is therefore consistent with the Stoner-Wohlfarth model.

Hysteresis branch crossing and the Stoner-Wohlfarth model.

The Stoner-Wohlfarth model predicts the crossing of the ascending and descending branches of the hysteretic magnetization curve. This crossing behavior has widely been dismissed, with the claim that it violates the laws of thermodynamics. Experimental verification of hysteresis branch crossing has not been acknowledged in the literature. Here we show, both theoretically and experimentally, that the crossing of the ascending and descending branches of the magnetization curve is a robust, reproducible phenomenon which does not violate any fundamental law.

Accurate quantitative phase digital holographic microscopy with single- and multiple-wavelength telecentric and nontelecentric configurations.

In this work, we investigate, both theoretically and experimentally, single-wavelength and multiwavelength digital holographic microscopy (DHM) using telecentric and nontelecentric configurations in transmission and reflection modes. A single-wavelength telecentric imaging system in DHM was originally proposed to circumvent the residual parabolic phase distortion due to the microscope objective (MO) in standard nontelecentric DHM configurations. However, telecentric configurations cannot compensate for higher order phase aberrations. As an extension to the telecentric and nontelecentric arrangements in single-wavelength DHM (SW-DHM), we propose multiple-wavelength telecentric DHM (MW-TDHM) in reflection and transmission modes. The advantages of MW-TDHM configurations are to extend the vertical measurement range without phase ambiguity and optically remove the parabolic phase distortion caused by the MO in traditional MW-DHM. These configurations eliminate the need for a second reference hologram to subtract the two-phase maps and make digital automatic aberration compensation easier to apply compared to nontelecentric configurations. We also discuss a reconstruction algorithm that eliminates the zero-order and virtual images using spatial filtering and another algorithm that minimizes the intensity of fluctuations using apodization. In addition, we employ two polynomial models using 2D surface fitting to compensate digitally for chromatic aberration (in the multiwavelength case) and for higher order phase aberrations. A custom-developed user-friendly graphical user interface is employed to automate the reconstruction processes for all configurations. Finally, TDHM is used to visualize cells from the highly invasive MDA-MB-231 cultured breast cancer cells.

Rapid prototyping of biomimetic vascular phantoms for hyperspectral reflectance imaging.

The emerging technique of rapid prototyping with three-dimensional (3-D) printers provides a simple yet revolutionary method for fabricating objects with arbitrary geometry. The use of 3-D printing for generating morphologically biomimetic tissue phantoms based on medical images represents a potentially major advance over existing phantom approaches. Toward the goal of image-defined phantoms, we converted a segmented fundus image of the human retina into a matrix format and edited it to achieve a geometry suitable for printing. Phantoms with vessel-simulating channels were then printed using a photoreactive resin providing biologically relevant turbidity, as determined by spectrophotometry. The morphology of printed vessels was validated by x-ray microcomputed tomography. Channels were filled with hemoglobin (Hb) solutions undergoing desaturation, and phantoms were imaged with a near-infrared hyperspectral reflectance imaging system. Additionally, a phantom was printed incorporating two disjoint vascular networks at different depths, each filled with Hb solutions at different saturation levels. Light propagation effects noted during these measurements­including the influence of vessel density and depth on Hb concentration and saturation estimates, and the effect of wavelength on vessel visualization depth­were evaluated. Overall, our findings indicated that 3-D-printed biomimetic phantoms hold significant potential as realistic and practical tools for elucidating light­tissue interactions and characterizing biophotonic system performance.

Spatially modulated laser pulses for printing electronics.

The use of a digital micromirror device (DMD) in laser-induced forward transfer (LIFT) is reviewed. Combining this technique with high-viscosity donor ink (silver nanopaste) results in laser-printed features that are highly congruent in shape and size to the incident laser beam spatial profile. The DMD empowers LIFT to become a highly parallel, rapidly reconfigurable direct-write technology. By adapting half-toning techniques to the DMD bitmap image, the laser transfer threshold fluence for 10 µm features can be reduced using an edge-enhanced beam profile. The integration of LIFT with this beam-shaping technique allows the printing of complex large-area patterns with a single laser pulse.

Monostatic all-fiber rangefinder system.

A rangefinder based on a fiber-coupled, monostatic system that transmits and receives through the same aperture has been developed. Some of the advantageous characteristics include elimination of the requirement for precision alignment of the receiver detector and smaller size than bistatic systems using separate transmit and receive apertures. Because there is no parallax between transmit and receive beam paths, optimum receiver alignment is maintained for all ranges. The system operates at 50 kpps and uses a 27 mm diameter/40 mm focal length transmit/receive lens. The standard deviation range precision of the system is 7.8 mm at 50 m with 3.3 µJ pulses.

Laser forward transfer using structured light.

A digital micromirror device (DMD) is used to spatially structure a 532 nm laser beam to print features spatially congruent to the laser spot in a laser-induced forward transfer (LIFT) process known as laser decal transfer (LDT). The DMD is a binary (on/off) spatial light modulator and its resolution, half-toning and beam shaping properties are studied using LDT of silver nanopaste layers. Edge-enhanced "checkerboard" beam profiles led to a ~30% decrease in the laser transfer fluence threshold (compared to a reference "checkerboard" profile) for a 20-pixel bitmap pattern and its resulting 10-µm square feature.

Reconfigurable acquisition system with integrated optics for a portable flow cytometer.

Portable and inexpensive scientific instruments that are capable of performing point of care diagnostics are needed for applications such as disease detection and diagnosis in resource-poor settings, for water quality and food supply monitoring, and for biosurveillance activities in autonomous vehicles. In this paper, we describe the development of a compact flow cytometer built from three separate, customizable, and interchangeable modules. The instrument as configured in this work is being developed specifically for the detection of selected Centers for Disease Control (CDC) category B biothreat agents through a bead-based assay: E. coli O157:H7, Salmonella, Listeria, and Shigella. It has two-color excitation, three-color fluorescence and light scattering detection, embedded electronics, and capillary based flow. However, these attributes can be easily modified for other applications such as cluster of differentiation 4 (CD4) counting. Proof of concept is demonstrated through a 6-plex bead assay with the results compared to a commercially available benchtop-sized instrument.

Quantitative transverse flow measurement using optical coherence tomography speckle decorrelation analysis.

We propose an inter-Ascan speckle decorrelation based method that can quantitatively assess blood flow normal to the direction of the optical coherence tomography imaging beam. To validate this method, we performed a systematic study using both phantom and in vivo animal models. Results show that our speckle analysis method can accurately extract transverse flow speed with high spatial and temporal resolution.

Microfluidics based phantoms of superficial vascular network.

Several new bio-photonic techniques aim to measure flow in the human vasculature non-destructively. Some of these tools, such as laser speckle imaging or Doppler optical coherence tomography, are now reaching the clinical stage. Therefore appropriate calibration and validation techniques dedicated to these particular measurements are therefore of paramount importance. In this paper we introduce a fast prototyping technique based on laser micromachining for the fabrication of dynamic flow phantoms. Micro-channels smaller than 20 µm in width can be formed in a variety of materials such as epoxies, plastics, and household tape. Vasculature geometries can be easily and quickly modified to accommodate a particular experimental scenario.

The role of Zn2+ on the structure and stability of murine adenosine deaminase.

Adenosine deaminase (ADA) is a key enzyme in purine metabolism and crucial for normal immune competence. It is a 40 kDa monomeric TIM-barrel protein containing a tightly bound Zn(2+), which is required for activity. In this study, we have investigated the role of Zn(2+) with respect to ADA structure and stability. After removing Zn(2+), the crystallographic structure of the protein remains highly ordered and similar to that of the holo protein with structural changes limited to regions capping the active site pocket. The stability of the protein, however, is decreased significantly in the absence of Zn(2+). Denaturation with urea shows the midpoint to be about 3.5 M for the apo enzyme, compared with 6.4 M for the holo enzyme. ADA contains four tryptophan residues distant from the Zn(2+) site. (19)F NMR studies in the presence and absence of Zn(2+) were carried out after incorporation of 6-(19)F-tryptophan. Chemical shift differences were observed for three of the four tryptophan residues, suggesting that, in contrast to the X-ray data, Zn(2+)-induced structural changes are propagated throughout the protein. Changes throughout the structure as suggested by the NMR data may explain the lower stability of the Zn(2+)-free protein. Real-time (19)F NMR spectroscopy measuring the loss of Zn(2+) showed that structural changes correlated with the loss of enzymatic activity.

Use of a multi-spectral camera in the characterization of skin wounds.

Skin breakdown is a prevalent and costly medical condition worldwide, with the etiologic and healing processes being complex and multifactorial. Quantitative assessment of wound healing is challenging due to the subjective measurement of wound size and related characteristics. We propose that in vivo spectral reflectance measurements can serve as valuable clinical monitoring tool/device in the study of wound healing. We have designed a multi spectral camera able to acquire 18 wavelength sensitive images in a single snapshot. A lenslets array in front of a digital camera is combined with narrowband filters (bandwidth 10 nm) ranging from 460 to 886 nm. Images taken with the spectroscopic camera are composed of 18 identical sub-images, each carrying different spectral information, that can be used in the assessment of skin chromophores. A clinical trial based on a repeated measures design was conducted at the National Rehabilitation Hospital on 15 individuals to assess whether Poly Carboxy Methyl Glucose Sulfate (PCMGS, CACIPLIQ20), a bio-engineered component of the extracellular matrix of the skin, is effective at promoting healing of a variety of wounds. Multi spectral images collected at different wavelengths combined with optical skin models were used to quantify skin oxygen saturation and its relation to the traditional measures of wound healing.

Design and fabrication of a low-cost, multispectral imaging system.

This paper reports the design and construction of a low-cost, multispectral imaging system using a single, large format CCD and an array of 18 individual lenses coupled to individual spectral filters. The system allows the simultaneous acquisition of 18 subimages, each with potentially different optical information. The subimages are combined to create a composite image, highlighting the desired spectral information. Because all the subimages are acquired simultaneously, the composite image shows no motion artifact. Although the present configuration uses 17 narrow bandpass optical filters to obtain multispectral information from a scene, the system is designed to be a general purpose, multiaperture platform, easily reconfigured for other multiaperture imaging modes.

Measurement of oxygen saturation in the retina with a spectroscopic sensitive multi aperture camera.

We introduce a new multi aperture system capable of capturing six identical images of the human fundus at six different spectral bands. The system is based on a lenslet array architecture and is well suited for spectroscopy application. The multi-aperture system was interfaced with a fundus camera to acquire spectroscopic sensitive images of the retina vessel and ultimately to calculate oxygen saturation in the retina in vivo. In vitro testing showed that the system is able to accurately reconstruct curves of partially oxygenated hemoglobin. In vivo testing on healthy volunteers was conducted and yielded results of oxygen saturation similar to the one reported in the literature, with arterial SO(2) approximately 0.95 and venous SO(2) approximately 0.5.

Design of cubic-phase optical elements using subwavelength microstructures.

We describe a design methodology for synthesizing cubic-phase optical elements using two-dimensional subwavelength microstructures. We combined a numerical and experimental approach to demonstrate that by spatially varying the geometric properties of binary subwavelength gratings it is possible to produce a diffractive element with a cubic-phase profile. A test element was designed and fabricated for operation in the LWIR, approximately lambda=10.6 microm. Experimental results verify the cubic-phase nature of the element.

Anticoagulation-related outcomes in patients receiving warfarin after starting levofloxacin or gatifloxacin.

STUDY OBJECTIVE: To compare anticoagulation-related outcomes in patients receiving stable dosages of warfarin who started levofloxacin or gatifloxacin therapy. DESIGN: Retrospective medical record review. SETTING: Veterans Affairs medical center. PATIENTS: Of 92 patients receiving the same dosages of warfarin for at least 4 weeks before starting antibiotic therapy, 54 received levofloxacin between January and September 2003, and 38 received gatifloxacin between January and September 2004. MEASUREMENTS AND MAIN RESULTS: Data were obtained through the hospital's pharmacy, laboratory, and general patient databases and through electronic medical records. The INRs evaluated were prefluoroquinolone use, defined as the last INR measured before the start of antibiotic therapy (up to 4 wks earlier), and postfluoroquinolone use, defined as any INR measured during antibiotic therapy through 1 week after discontinuation of the antibiotic. Analyzed outcomes included the percentage of patients with postfluoroquinolone INRs that were above 4, that exceeded the therapeutic goal, or that exceeded the goal by more than 1 point; INR changes of more than 0.5, 1, or 1.5 points above the INR before fluoroquinolone use; major or minor bleeding events; requirement for vitamin K administration; warfarin dosage reduction or withholding doses; and warfarin-related hospital, emergency, or urgent care admissions or visits. No significant differences were noted in baseline characteristics with regard to age, sex, prefluoroquinolone INR, or anticoagulation indications between the two groups. The percentage of patients with a postfluoroquinolone INR above 4 was 2% (1 of 54 patients) in the levofloxacin group versus 21% (8 of 38 patients) in the gatifloxacin group (p=0.003). The percentage of patients receiving vitamin K in the levofloxacin and gatifloxacin groups was 0% (0 of 54 patients) and 11% (4 of 38, p=0.026), respectively. For the other anticoagulation-related outcomes, no significant differences were noted between the groups. CONCLUSION: Patients receiving warfarin who take gatifloxacin may be at higher risk for an INR above 4 compared with those taking levofloxacin. Close monitoring of warfarin therapy while concomitantly receiving gatifloxacin is warranted.