A Process Planning Method and Data Format for Achieving Tolerances in Stereolithography

When building parts in a stereolithography apparatus (SLA), the user is faced with many decis!ons regarding the setting of process variables. To 'achieve a set of tolera~ces as closely as pOSSIble, relationships between part geometry, tolerances, and process v~nables ~ust be understood quantitatively. This paper presents a method for SLA process plannIng that IS based on response surface methodology and multi-objective optimization, where the response surfaces capture these relationships. These response surfaces were generated by extensive design-of-experiment studies for a variety of geometries. An annotated STL data format is also presented that enables the inclusion of tolerance and surface information in fatetted representations. Application of the data format and process planning method is illustrated on one part.Mechanical Engineerin

The Dynamics of EEG Entropy

EEG time series are analyzed using the diffusion entropy method. The resulting EEG entropy manifests short-time scaling, asymptotic saturation and an attenuated alpha-rhythm modulation. These properties are faithfully modeled by a phenomenological Langevin equation interpreted within a neural network context

Techniques for achieving magnetic cleanliness on deep-space missions

Techniques for obtaining magnetic cleanliness on deep space missions to allow interplanetary magnetic field mappin

Probing the Melting of a Two-dimensional Quantum Wigner Crystal via its Screening Efficiency

One of the most fundamental and yet elusive collective phases of an interacting electron system is the quantum Wigner crystal (WC), an ordered array of electrons expected to form when the electrons' Coulomb repulsion energy eclipses their kinetic (Fermi) energy. In low-disorder, two-dimensional (2D) electron systems, the quantum WC is known to be favored at very low temperatures ($T$) and small Landau level filling factors ($\nu$), near the termination of the fractional quantum Hall states. This WC phase exhibits an insulating behavior, reflecting its pinning by the small but finite disorder potential. An experimental determination of a $T$ vs $\nu$ phase diagram for the melting of the WC, however, has proved to be challenging. Here we use capacitance measurements to probe the 2D WC through its effective screening as a function of $T$ and $\nu$. We find that, as expected, the screening efficiency of the pinned WC is very poor at very low $T$ and improves at higher $T$ once the WC melts. Surprisingly, however, rather than monotonically changing with increasing $T$, the screening efficiency shows a well-defined maximum at a $T$ which is close to the previously-reported melting temperature of the WC. Our experimental results suggest a new method to map out a $T$ vs $\nu$ phase diagram of the magnetic-field-induced WC precisely.Comment: The formal version is published on Phys. Rev. Lett. 122, 116601 (2019

Magnetoresistance Oscillations in Two-dimensional Electron Systems Induced by AC and DC Fields

We report on magnetotransport measurements in a high-mobility two-dimentional electron system subject simultaneously to AC (microwave) and DC (Hall) fields. We find that DC excitation affects microwave photoresistance in a nontrivial way. Photoresistance maxima (minima) evolve into minima (maxima) and back, reflecting strong coupling and interplay of AC- and DC-induced effects. Most of our observations can be explained in terms of indirect electron transitions using a new, ``combined'' resonant condition. Observed quenching of microwave-induced zero resistance by a DC field cannot be unambiguously linked to a domain model, at least until a systematic theory treating both excitation types within a single framework is developed

Surface segregation and the Al problem in GaAs quantum wells

Low-defect two-dimensional electron systems (2DESs) are essential for studies of fragile many-body interactions that only emerge in nearly-ideal systems. As a result, numerous efforts have been made to improve the quality of modulation-doped Al$_x$Ga$_{1-x}$As/GaAs quantum wells (QWs), with an emphasis on purifying the source material of the QW itself or achieving better vacuum in the deposition chamber. However, this approach overlooks another crucial component that comprises such QWs, the Al$_x$Ga$_{1-x}$As barrier. Here we show that having a clean Al source and hence a clean barrier is instrumental to obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the 2DES in GaAs QWs declines as the thickness or Al content of the Al$_x$Ga$_{1-x}$As barrier beneath the QW is increased, which we attribute to the surface segregation of Oxygen atoms that originate from the Al source. This conjecture is supported by the improved mobility in the GaAs QWs as the Al cell is cleaned out by baking

Low-cost interactive active monocular range finder

This paper describes a low-cost interactive active monocular range finder and illustrates the effect of introducing interactivity to the range acquisition process. The range finder consists of only one camera and a laser pointer, to which three LEDs are attached. When a user scans the laser along surfaces of objects, the camera captures the image of spots (one from the laser, and the others from LEDs), and triangulation is carried out using the camera\u27s viewing direction and the optical axis of the laser. The user interaction allows the range finder to acquire range data in which the sampling rate varies across the object depending on the underlying surface structures. Moreover, the processes of separating objects from the background and/or finding parts in the object can be achieved using the operator\u27s knowledge of the objects

Coulomb Oscillations in Antidots in the Integer and Fractional Quantum Hall Regimes

We report measurements of resistance oscillations in micron-scale antidots in both the integer and fractional quantum Hall regimes. In the integer regime, we conclude that oscillations are of the Coulomb type from the scaling of magnetic field period with the number of edges bound to the antidot. Based on both gate-voltage and field periods, we find at filling factor {\nu} = 2 a tunneling charge of e and two charged edges. Generalizing this picture to the fractional regime, we find (again, based on field and gate-voltage periods) at {\nu} = 2/3 a tunneling charge of (2/3)e and a single charged edge.Comment: related papers at http://marcuslab.harvard.ed

Bilayer Quantum Hall Systems at nuT = 1: Coulomb Drag and the Transition from Weak to Strong Interlayer Coupling

Measurements revealing anomalously large frictional drag at the transition between the weakly and strongly coupled regimes of a bilayer two-dimensional electron system at total Landau level filling factor nuT = 1 are reported. This result suggests the existence of fluctuations, either static or dynamic, near the phase boundary separating the quantized Hall state at small layer separations from the compressible state at larger separations. Interestingly, the anomalies in drag seem to persist to larger layer separations than does interlayer phase coherence as detected in tunneling