Do as the Neighbors Do: The Impact of Social Networks on Immigrant Employees

Substantial immigrant segregation in the United States, combined with the increase in the share of the U.S. foreign-born population, have led to great interest in the causes and consequences of immigrant concentration, including those related to the functioning of labor markets. This paper provides robust evidence that both the size and the quality of an immigrant enclave affects the labor market outcomes of new immigrants. We develop new measures of the quality, or information value, of immigrant networks by exploiting data based on worker earnings records matched to firm and Census information. We demonstrate the importance of immigrant employment links: network members are much more likely than other immigrants to be employed in the same firm as their geographic neighbors. Immigrants living with large numbers of employed neighbors are more likely to have jobs than immigrants in areas with fewer employed neighbors. The effects are quantitatively important and robust under alternative specifications. For example, in a high value network – one with an average employment rate in the 90th percentile – a one standard deviation increase in the log of the number of contacts in the network is associated with almost a 5% increase in the employment rate. Earnings, conditional on employment, increase by about 0.7%.Social networks, immigrant enclaves, labor market intermediaries

All-Pay Auctions with Pre- and Post-Bidding Options

Motivated by the emergence of online penny or pay-to-bid auctions, in this study, we analyze the operational consequences of all-pay auctions competing with fixed list price stores. In all-pay auctions, bidders place bids, and highest bidder wins. Depending on the auction format, the winner pays either the amount of their bid or that of the second-highest bid. All losing bidders forfeit their bids, regardless of the auction format. Bidders may visit the store, both before and after bidding, and buy the item at the fixed list price. In a modified version, we consider a setting where bidders can use their sunk bid as a credit towards buying the item from the auctioneer at a fixed price (different from the list price). We characterize a symmetric equilibrium in the bidding/buying strategy and derive optimal list prices for both the seller and auctioneer to maximize expected revenue. We consider two situations: (1) one firm operating both channels (i.e. fixed list price store and all-pay auction), and (2) two competing firms, each operating one of the two channels

Near BER optimal partial response codes

Partial response signaling (PRS) codes with maximal minimum Euclidean distance have previously been found by linear programming. These perform very well in the narrowband-high energy region, but they were not optimized for minimal bit error rate (BER), so they are only optimal in the limit of infinite signal to noise ratio. Here we search for codes that perform better for more practical signal to noise ratios. The BER objective function is no longer linear, but it is still conve

Constrained capacities for faster-than-Nyquist signaling

This paper deals with capacity computations of faster-than-Nyquist (FTN) signaling. It shows that the capacity of FTN is higher than the orthogonal pulse linear modulation capacity for all pulse shapes except the sinc. FTN signals can in fact achieve the ultimate capacity for the signal power spectral density (PSD). The paper lower and upper bounds the FTN capacity under the constraint of finite input alphabet. It is often higher than the capacity for comparable orthogonal pulse systems; sometimes it is superior to all forms of orthogonal signaling with the same PSD

Multistream faster than Nyquist signaling

We extend Mazo's concept of faster-than-Nyquist (FTN) signaling to pulse trains that modulate a bank of subcarriers, a method called two dimensional FTN signaling. The signal processing is similar to orthogonal frequency division multiplex (OFDM) transmission but the subchannels are not orthogonal. Despite nonorthogonal pulses and subcarriers, the method achieves the isolated-pulse error performance; it does so in as little as half the bandwidth of ordinary OFDM. Euclidean distance properties are investigated for schemes based on several basic pulses. The best have Gaussian shape. An efficient distance calculation is given. Concatenations of ordinary codes and FTN are introduced. The combination achieves the outer code gain in as little as half the bandwidth. Receivers must work in two dimensions, and several iterative designs are proposed for FTN with outer convolutional coding

Serial and parallel concatenations based on faster than Nyquist signaling

We investigate the performance of concatenated coding schemes based on Faster Than Nyquist(FTN) signaling over the AWGN channel. We test both serial and parallel concatenations. In serial concatenation the FTN signaling is considered as the inner encoder and the outer code is a rate b/c convolutional code. In parallel schemes we use two parallel Gaussian channels and transmit FTN pulse trains in both; here a precoding device turns out to be crucial. The convergence behaviour is analysed using EXIT charts. The overall spectral density of the schemes varies but is roughly 1–2 bit/s/Hz. The results, in terms of needed Eb/N0 for reliable communication versus spectral density, are very good

Successive interference cancellation in multistream faster-than-Nyquist Signaling

In earlier work we have extended Mazo's concept of faster-than-Nyquist signaling to pulse trains that modulate adjacent subcarriers, a method we called two dimensional Mazo signaling. The signal processing is similar to orthogonal frequency division multiplex (OFDM) transmission. Despite pulses that are faster than the Nyquist limit and subcarriers that significantly overlap, the transmission achieves the isolated pulse error performance. In this paper we review the method and test a receiver based on successive interference cancellation. It virtually achieves the matched filter bound

Receivers for faster-than-Nyquist signaling with and without turbo equalization

Faster-than-Nyquist (FTN) signaling is a trellis coding method that maintains the error rate while reducing signal bandwidth. The combined effect is to move closer to capacity. We study some basic receiver issues: How to model the signaling efficiently in discrete time, how much the Viterbi receiver can be truncated, and how to combine the method with an outer code. The methods are modeling for minimum phase, minimum distance calculation and receiver tests. Concatenated FTN in a turbo equalization scenario proves to be a strong coding method

New reduced state space BCJR algorithms for the ISI channel

A critical component in detection under intersymbol interference (ISI) and in turbo equalization is the BCJR algorithm. We study two approaches to reducing its computation. First, the state space is reduced by optimizing the receiver's phase-maximizing all pass filter. Then the state space used by the BCJR calculation is reduced by breaking the state into an offset and a main state. These procedures are demonstrated by ISI detection and turbo equalization over strongly bandlimited channels

Host-dependent larval migration and parasitism risk in a polyphagous moth

Female herbivorous insects are expected to oviposit on the host plant providing the best performance of the offspring. However, in some insects the larvae are mobile and are not totally dependent on the mother's choice. They can change host plant when conditions for development or exposure to natural enemies vary between individual plants within a patch. Here we study larval migration and preference between two host plants, cotton and alfalfa, in the Egyptian leafworm, Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae). Previous studies have shown that although larval performance is better on cotton, females prefer to oviposit on alfalfa, and this preference corresponds to a higher survival of the eggs. In this study, S. littoralis larvae showed directed movement between host plants and were found to prefer alfalfa over cotton in field test in Egypt, as well as in laboratory selection of feeding site assays. To determine effects by natural enemies, the parasitism rates and various life-history traits were measured for one larval parasitoid, Microplitis rufiventris Kokujev (Hymenoptera: Braconidae), on several host plants including cotton and clover (equivalent host plant to alfalfa). Overall, parasitism was higher on cotton and parasitoid performance (cocoon mass, adult longevity, and female egg load) was better on cotton compared to clover. This fact suggests an enemy-free space on clover and alfalfa, as parasitism rate is higher on cotton, and the parasitoid performance is also better on cotton-fed larvae.Larval migration was investigated in the Egyptian leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae). Larvae showed directed movement between host plants and were found to prefer alfalfa over cotton in field and laboratory tests, even though larval performance is better on cotton. However, parasitism rates were higher and parasitoid performance (cocoon mass, adult longevity, and female egg load) was better for the larval parasitoid Microplitis rufiventris (Hymenoptera: Braconidae) on cotton, suggesting enemy-free space on alfalfa.imag