Solder paste mixture

A solder paste is composed of a vehicle (or flux) system and a mixture of at least two solder powders. One component of this mixture is a eutectic or near-eutectic Sn/Pb alloy powder, while the other component comprises powders selected from at least one elemental metal powder or at least one solder alloy powder or at least one elemental metal powder and at least one solder alloy powder. Said other component is a powder or combination of powders each of which has a liquidus temperature which is lower by at least 5 degrees Centigrade (°C.) than the solidus temperature of said eutectic or near-eutectic Sn/Pb alloy powder or a solidus temperature which is higher by at least 5° C. than the liquidus temperature of said eutectic or near-eutectic Sn/Pb alloy powder. The eutectic or near-eutectic Sn/Pb powder makes up from 5 to 95 weight percent of the total powder mixture. Alternatively, not all powders which comprise the second component need to obey this rule so long as at least 30% by wt. of the entire powder mixture has a solidus temperature which is at least 5° C. higher than the highest liquidus temperature of the eutectic or near-eutectic Sn/Pb alloy powder. This solder paste results in an uncompromised consolidation and wetting process in which all of the solder joints or balls are formed on and wetted to an appropriate contact by the solder reflow process.Published versio

Quantum control theory for coupled 2-electron dynamics in quantum dots

We investigate optimal control strategies for state to state transitions in a model of a quantum dot molecule containing two active strongly interacting electrons. The Schrodinger equation is solved nonperturbatively in conjunction with several quantum control strategies. This results in optimized electric pulses in the THz regime which can populate combinations of states with very short transition times. The speedup compared to intuitively constructed pulses is an order of magnitude. We furthermore make use of optimized pulse control in the simulation of an experimental preparation of the molecular quantum dot system. It is shown that exclusive population of certain excited states leads to a complete suppression of spin dephasing, as was indicated in Nepstad et al. [Phys. Rev. B 77, 125315 (2008)].Comment: 24 pages, 9 figure

Perturbation theory for the one-dimensional optical polaron

The one-dimensional optical polaron is treated on the basis of the perturbation theory in the weak coupling limit. A special matrix diagrammatic technique is developed. It is shown how to evaluate all terms of the perturbation theory for the ground-state energy of a polaron to any order by means of this technique. The ground-state energy is calculated up to the eighth order of the perturbation theory. The effective mass of an electron is obtained up to the sixth order of the perturbation theory. The radius of convergence of the obtained series is estimated. The obtained results are compared with the results from the Feynman polaron theory.Comment: 9 pages, 2 figures, RevTeX, to be published in Phys. Rev. B (2001) Ap

Extreme Harmonic Generation in Electrically Driven Spin Resonance

We report the observation of multiple harmonic generation in electric dipole spin resonance in an InAs nanowire double quantum dot. The harmonics display a remarkable detuning dependence: near the interdot charge transition as many as eight harmonics are observed, while at large detunings we only observe the fundamental spin resonance condition. The detuning dependence indicates that the observed harmonics may be due to Landau-Zener transition dynamics at anticrossings in the energy level spectrum.Comment: Related papers at http://pettagroup.princeton.ed

Insect pollination as an agronomic input: strategies for oilseed rape production

1.Ecological intensification involves the incorporation of biodiversity based ecosystem service management into farming systems in order to make crop production more sustainable and reduce reliance on anthropogenic inputs, including fertiliser and insecticides. 2.The benefits of effectively managing ecosystem services such as pollination and pest regulation for improved yields have been demonstrated in a number of studies, however recent evidence indicates that these benefits interact with conventional agronomic inputs such as fertiliser and irrigation. Despite the important contribution of biodiversity‐based ecosystem services to crop production their management is rarely considered in combination with more conventional agronomic inputs. 3.This study combines a number of complementary approaches to evaluate the impact of insect pollination on yield parameters of Brassica napus and how this interacts with a key agronomic input, fertiliser. We incorporate data from a flight cage trial and multiple field studies to quantify the relationships between yield parameters to determine whether insufficient insect pollination may limit crop yield. 4.We demonstrate that, by producing larger seeds and more pods, B. napus has the capacity to modulate investment across yield parameters and buffer sub‐optimal inputs of fertiliser or pollination. However, only when fertiliser is not limiting can the crop benefit from insect pollination, with yield increases due to insect pollination only seen under high fertiliser application. 5.A non‐linear relationship between seed set per pod and yield per plant was found, with increases in seed set between 15 and 25 seeds per pod resulting in a consistent increase in crop yield. The capacity for the crop to compensate for lower seed set due to sub‐optimal pollination is therefore limited. 6.Synthesis and applications. Oilseed rape has the capacity to compensate for sub‐optimal agronomic or ecosystem service inputs although this has limitations. Insect pollination can increase seed set and so there are production benefits to be gained through effective management of wild pollinators or by utilising managed species. Our study demonstrates however that increased insect pollination cannot simply replace other inputs, and if resources such as fertiliser are limiting, then yield potential cannot be reached. We highlight the need to consider insect pollination as an agronomic input to be effectively managed in agricultural systems

On the Construction of Human-Automation Interfaces by Formal Abstraction

In this paper we present a formal methodology and an algorithmic procedure for constructing human-auto-mation interfaces and corresponding user-manuals. Our focus is the information provided to the user about the behavior of the underlying machine, rather than the graphical and layout features of the interface itself. Our approach involves a systematic reduction of the behavioral model of the machine, as well as systematic abstraction of information that displayed in the inter-face. This reduction procedure satisfies two require-ments: First, the interface must be correct so as not to cause mode confusion that may lead the user to per-form incorrect actions. Secondly, the interface must be as simple as possible and not include any unnecessary information. The algorithm for generating such inter-faces can be automated, and a preliminary software system for its implementation has been developed

The basic mechanics of bipedal walking lead to asymmetric behavior

Abstract-This paper computationally investigates whether gait asymmetries can be attributed in part to basic bipedal mechanics independent of motor control. Using a symmetrical rigid-body model known as the compass-gait biped, we show that changes in environmental or physiological parameters can facilitate asymmetry in gait kinetics at fast walking speeds. In the environmental case, the asymmetric family of high-speed gaits is in fact more stable than the symmetric family of lowspeed gaits. These simulations suggest that lower extremity mechanics might play a direct role in functional and pathological asymmetries reported in human walking, where velocity may be a common variable in the emergence and growth of asymmetry

Polaron effects in electron channels on a helium film

Using the Feynman path-integral formalism we study the polaron effects in quantum wires above a liquid helium film. The electron interacts with two-dimensional (2D) surface phonons, i.e. ripplons, and is confined in one dimension (1D) by an harmonic potential. The obtained results are valid for arbitrary temperature ($T$), electron-phonon coupling strength ($\alpha$), and lateral confinement ($\omega_{0}$). Analytical and numerical results are obtained for limiting cases of $T$, $\alpha$, and $\omega_{0}$. We found the surprising result that reducing the electron motion from 2D to quasi-1D makes the self-trapping transition more continuous.Comment: 6 pages, 7 figures, submitted to Phys. Rev.