In 1961, Svensson described isoelectric focusing (IEF), the separation of ampholytic compounds in a stationary, natural pH gradient that was formed by passing current through a sucrose density ...gradient‐stabilized ampholyte mixture in a constant cross‐section apparatus, free of mixing. Stable pH gradients were formed as the electrophoretic transport built up a series of isoelectric ampholyte zones—the concentration of which decreased with their distance from the electrodes—and a diffusive flux which balanced the generating electrophoretic flux. When polyacrylamide gel replaced the sucrose density gradient as the stabilizing medium, the spatial and temporal stability of Svensson's pH gradient became lost, igniting a search for the explanation and mitigation of the loss. Over time, through a series of insightful suggestions, the currently held notion emerged that in the modern IEF experiment—where the carrier ampholyte (CA) mixture is placed between the anolyte‐ and catholyte‐containing large‐volume electrode vessels (open‐system IEF)—a two‐stage process operates that comprises a rapid first phase during which a linear pH gradient develops, and a subsequent slow, second stage, during which the pH gradient decays as isotachophoretic processes move the extreme pI CAs into the electrode vessels. Here we trace the development of the two‐stage IEF model using quotes from the original publications and point out critical results that the IEF community should have embraced but missed. This manuscript sets the foundation for the companion papers, Parts 2 and 3, in which an alternative model, transient bidirectional isotachophoresis is presented to describe the open‐system IEF experiment.
Eddy current sensors are extensively utilized across various nondestructive testing (NDT) applications. The idea of magnetic field focusing (MFF) is to constrain the magnetic field distribution ...within a certain area for spatial resolution improvement in imaging. In eddy current testing (ECT), the sensitivity distribution is not only related to the excitation field but also to the receiving field. Therefore, the focusing of both magnetic fields toward the designated area has the potential to focus sensitivity distribution, thus improving spatial resolution in defect imaging. This article defines the "focus area" of sensitivity and investigates sensitivity focusing in ECT through coil angle variation. Magnetic fields from a single coil of different tilt angles are calculated based on the second order vector potential (SOVP) approach and the 2-D Fourier Transform. The sensitivity to permeability for one pair of coils is investigated and the focus areas of different coil systems are evaluated. Numerical and experimental results prove that higher spatial resolutions on permeability perturbations (sensitivity focusing for permeability variation) are feasible by changing the coil tilt angles.
Imaged capillary isoelectric focusing (iCIEF) has emerged as an important technique for therapeutic monoclonal antibody (mAb) charge heterogeneity analysis in the biopharmaceutical context, providing ...imaged detection and quantitation by UV without a mobilization step. Besides quantitation, the characterization of separated charge variants ideally directly by online electrospray ionization–mass spectrometry (ESI–MS) is crucial to ensure product quality, safety, and efficacy. Straightforward direct iCIEF–MS coupling combining high separation efficiency and quantitative results of iCIEF with the characterization power of MS enables deep characterization of mAb charge variants. A short technical setup and optimized methodical parameters (30 nl/min mobilization rate, 2%–4% ampholyte concentration, 0.5–2 mg/ml sample concentration) allow successful mAb charge variant peak assignment from iCIEF to MS. Despite a loss of separation resolution during the transfer, separated intact mAb charge variants, including deamidation as well as major and minor glycoforms even from low abundant charge variants, could be characterized by online ESI–MS with high precision. The presented setup provides a large potential for mAb charge heterogeneity characterization in biopharmaceutical applications.
Manipulation of the propagation and energy‐transport characteristics of subwavelength infrared (IR) light fields is critical for the application of nanophotonic devices in photocatalysis, biosensing, ...and thermal management. In this context, metamaterials are useful composite materials, although traditional metal‐based structures are constrained by their weak mid‐IR response, while their associated capabilities for optical propagation and focusing are limited by the size of attainable artificial optical structures and the poor performance of the available active means of control. Herein, a tunable planar focusing device operating in the mid‐IR region is reported by exploiting highly oriented in‐plane hyperbolic phonon polaritons in α‐MoO3. Specifically, an unprecedented change of effective focal length of polariton waves from 0.7 to 7.4 μm is demonstrated by the following three different means of control: the dimension of the device, the employed light frequency, and engineering of phonon–plasmon hybridization. The high confinement characteristics of phonon polaritons in α‐MoO3 permit the focal length and focal spot size to be reduced to 1/15 and 1/33 of the incident wavelength, respectively. In particular, the anisotropic phonon polaritons supported in α‐MoO3 are combined with tunable surface‐plasmon polaritons in graphene to realize in situ and dynamical control of the focusing performance, thus paving the way for phonon‐polariton‐based planar nanophotonic applications.
A planar polariton focusing device based on the natural in‐plane hyperbolic van der Waals material α‐MoO3 is developed, which achieves ultrahigh field compression and wide‐range tunable performance. Moreover, a graphene/α‐MoO3 heterostructure is constructed, which supports hybrid modes consisting of α‐MoO3 phonon polaritons and graphene plasmons to achieve in situ dynamical control of the focal length.
The synthesis of frequency diverse arrays (FDAs) able to achieve time-invariant spatial focusing performance in the short-range is addressed. Two time-modulated optimized frequency offset schemes are ...presented that allow focusing the energy at a single target location and multiple target locations, respectively. A set of numerical examples is reported and discussed to validate the effectiveness of the proposed solutions also in comparison with the already proposed FDA design approaches.
Metasurfaces enable a new paradigm to control electromagnetic waves by manipulating subwavelength artificial structures within just a fraction of wavelength. Despite the rapid growth, simultaneously ...achieving low‐dimensionality, high transmission efficiency, real‐time continuous reconfigurability, and a wide variety of reprogrammable functions is still very challenging, forcing researchers to realize just one or few of the aforementioned features in one design. This study reports a subwavelength reconfigurable Huygens' metasurface realized by loading it with controllable active elements. The proposed design provides a unified solution to the aforementioned challenges of real‐time local reconfigurability of efficient Huygens' metasurfaces. As one exemplary demonstration, a reconfigurable metalens at the microwave frequencies is experimentally realized, which, to the best of the knowledge, demonstrates for the first time that multiple and complex focal spots can be controlled simultaneously at distinct spatial positions and reprogrammable in any desired fashion, with fast response time and high efficiency. The presented active Huygens' metalens may offer unprecedented potentials for real‐time, fast, and sophisticated electromagnetic wave manipulation such as dynamic holography, focusing, beam shaping/steering, imaging, and active emission control.
By loading controllable active elements, a subwavelength metasurface is proposed with real‐time local reconfigurability. A reconfigurable active Huygens' metalens is experimentally realized at microwave frequencies, which demonstrates for the first time that multiple and complex focal spots can be controlled simultaneously at distinct spatial positions and reprogrammable in any desired fashion, with a fast response time of 10 µs and high efficiency.
CE is central to the analysis, process development and approval of therapeutic monoclonal antibodies (mAbs). Recently, imaged capillary isoelectric focusing (icIEF) has emerged as a powerful ...technique for quantitative protein charge heterogeneity monitoring and characterization, particularly for mAbs. However, icIEF has yet to be validated for therapeutically relevant mAbs adhering to the ICH guideline (International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use). Here, for the first time, icIEF technology was validated by 10 laboratories across 8 independent companies using a therapeutic mAb. The parameters of this method validation strictly follow the guideline of the ICH. This guideline includes specificity, precision, accuracy, linearity, range, LOQ and robustness. These results represent a significant step forward in standardizing the use of icIEF methods for the clinical approval of therapeutic mAbs.
We address the problem of estimating target locations that are sparse in a pulse-Doppler radar's unambiguous region by sampling the received signal at sub-Nyquist rates. The received signal is ...modeled as a finite-rate-of-innovation (FRI) signal, and the problem of estimating the delays in a single transceiver radar is formulated as one of recovery of sparse common-support (SCS) FRI signals, which arises in the context of channel estimation in multiple input, multiple output communication systems. The delays are estimated by the SCS-FRI reconstruction method. We present a new method termed delay focusing to estimate the Doppler shifts. To obtain overall performance gains, we also present an extended method called dual focusing, which combines both delay and Doppler focusing schemes, and has the capability to superresolve targets in the delay-Doppler plane. The performance of the recovery methods in the presence of noise is also analyzed. We demonstrate that the proposed estimation methods are robust to noise. Monte Carlo performance analysis in the presence of noise shows that the dual focusing method accurately resolves closely spaced targets and yields a significant decrease in normalized mean-square error of up to 10-20 dB for the estimated Doppler shifts. We also simulate the scenario where multiple targets are in a formation, that is, when they are closely spaced along both delay and Doppler axes, and show that the dual focusing method achieves a hit rate of nearly 100% at a much lower signal-to-noise ratios than that required for Doppler focusing.
PDF
