Tuning the thermoresponsive properties of poly(oligo(propylene glycol) methacrylate) hydrogels via gradient copolymerization with 2-hydroxyethyl methacrylate

Gamma radiation was used to prepare copolymer hydrogel libraries based on oligo(propylene glycol) methacrylate (OPGMA) and 2-hydroxyethyl methacrylate (HEMA); a complete screening in composition of P(OPGMA/HEMA) copolymers was elaborated from 0% to 100% of OPGMA. Determination of gel fraction was performed as the first step after radiation induced synthesis. Tuning of the volume phase transition temperature (VPTT) of P(OPGMA/HEMA) copolymeric hydrogels was investigated by swelling study. Additional characterization of structure and properties was conducted by FTIR, DSC, and UV-Vis spectroscopy. All results indicate that new P(OPGMA/HEMA) copolymeric hydrogels have wide diversity in thermoresponsive properties which strongly depend on their composition.     

High-resolution and tandem mass spectrometry--the indispensable tools of the XXI century

Mass spectrometry-based qualitative and quantitative (bio)molecular analysis is a corner stone in the state-of-the-art pipelines in systems biology and environmental sciences. High-resolution and efficient tandem mass spectrometry methods and techniques are the essential analytical capabilities for the in-depth analysis of extremely complex mixtures of (bio)molecules of a very broad dynamic range of concentrations. Here, we briefly review the advantages and limitations of the current mass spectrometry with a focus on resolution, or resolving power, and methods of (bio)molecular fragmentation in the gas phase. We conclude with an outlook that considers possible avenues for further mass spectrometry-based method and technique development, indispensable for advancing the challenging real-life mass spectrometry applications in the XXI century.     

Hot topics for mobile services

Upcoming mobile technologies like the Universal Mobile Telecommunications System (UMTS) or Voice-Over-IP/IP Multimedia Subsystem (VoIP/IMS) offer new possibilities but also threats. Consequently, operators and vendors need to adopt appropriate technology and business principles. This article focuses on the concept of Service Platforms to allow flexible and fast service development, and enablers for Location Based Services.     

Using PARLAY APIs Over a SIP System in a Distributed Service Platform for Carrier Grade Multimedia Services

The implementation of new mobile communication technologies developed in the third generation partnership project (3GPP) will allow to access the Internet not only from a PC but also via mobile phones, palmtops and other devices. New applications will emerge, combining several basic services like voice telephony, e-mail, voice over IP, mobility or web-browsing, and thus wiping out the borders between the fixed telephone network, mobile radio and the Internet. Offering those value-added services will be the key factor for success of network and service providers in an increasingly competitive market. In 3GPP's service framework the use of the Parlay APIs is proposed that allow application development by third parties in order to speed up service creation and deployment. 3GPP has also adopted SIP for session control of multimedia communications in an IP network. This article proposes a mapping of SIP functionality to Parlay services and describes a prototype implementation using the SIP Servlet API. Furthermore, an architecture of a Service Platform is presented that offers a framework for the creation, execution and management of carrier grade multimedia services in heterogeneous networks.     

Generalized LDPC codes and generalized stopping sets

A generalized low-density parity check code (GLDPC) is a low-density parity check code in which the constraint nodes of the code graph are block codes, rather than single parity checks. In this paper, we study GLDPC codes which have BCH or Reed-Solomon codes as subcodes under bounded distance decoding (BDD). The performance of the proposed scheme is investigated in the limit case of an infinite length (cycle free) code used over a binary erasure channel (BEC) and the corresponding thresholds for iterative decoding are derived. The performance of the proposed scheme for finite code lengths over a BEC is investigated as well. Structures responsible for decoding failures are defined and a theoretical analysis over the ensemble of GLDPC codes which yields exact bit and block error rates of the ensemble average is derived. Unfortunately this study shows that GLDPC codes do not compare favorably with their LDPC counterpart over the BEC. Fortunately, it is also shown that under certain conditions, objects identified in the analysis of GLDPC codes over a BEC and the corresponding theoretical results remain useful to derive tight lower bounds on the performance of GLDPC codes over a binary symmetric channel (BSC). Simulation results show that the proposed method yields competitive performance with a good decoding complexity trade-off for the BSC.     

Comparison of the ion exchange uptake of ammonium ion onto New Zealand clinoptilolite and mordenite

In this study the uptake performances of the naturally occurring zeolite, clinoptilolite, and of New Zealand mordenite are compared. The uptake of fully ionised ammonium ion from aqueous solutions in the concentration range 0–200 mg/l on to these two materials was compared. The influence of other cations present in water upon the ammonia uptake was also determined. The cations studied were potassium, calcium and magnesium. In all cases the anionic counterion present was chloride. The results showed that the mordenite exhibited higher overall uptake concentrations at equilibrium compared with clinoptilolite at solution concentrations greater than 80 mg/l. Beyond this value, the difference in solid-phase equilibrium concentrations on the mordenite became greater at higher solution-phase ammonium ion concentrations. The effect of the other cations upon uptake of ammonium ion was relatively small. In all cases, the ammonium ion showed the highest uptake on to both the mordenite and the clinoptilolite. In the case of clinoptilolite this was rather an unexpected result since the majority of other work shows clinoptilolite exhibiting a higher affinity for potassium ion compared with ammonium ion. This may be explained by the fact that the clinoptilolite came from volcanic deposits in New Zealand. This is the first such study on this material. At solution-phase equilibrium concentrations of greater than 80 mg/l, the mordenite showed smaller reductions in ammonium ion uptake in the presence of the other cations when compared with clinoptilolite.     

Irregular LDPC codes as concatenation regular LDPC codes

In this letter, the construction of irregular LDPC codes obtained by concatenating regular ones is considered. These codes are analyzed for the binary symmetric channel (BSC). It is shown via proper distribution evolution that such concatenated codes have in general a threshold value weaker (but not necessarily much different) than their unconstrained counterparts for the BSC. On the other hand, they can offer advantages in term of convergence and error performance for lengths of practical interest and long enough to validate the degree distribution selection.     

Systematic recursive construction of LDPC codes

This letter presents a systematic and recursive method to construct good low-density parity-check (LDPC) codes, especially those with high rate. The proposed method uses a parity check matrix of a quasi-cyclic LDPC code with given row and column weights as a core upon which the larger code is recursively constructed with extensive use of pseudorandom permutation matrices. This construction preserves the minimum distance and girth properties of the core matrix and can generate either regular, or irregular LDPC codes. The method provides a unique representation of the code in compact notation.     

Temperature/pH dual responsive OPGMA based copolymeric hydrogels prepared by gamma radiation: an optimisation study

The purpose of this study was to attain oligo(propylene glycol) methacrylate (OPGMA) based hydrogels for different biomedical applications. Since the volume phase transition temperature (VPTT) of poly(oligo(propylene glycol) methacrylate) (POPGMA) homopolymer was below room temperature, it was necessary to tune the thermoresponsiveness and the VPTT to higher temperatures; radical copolymerisation of OPGMA with more hydrophilic and/or pH responsive monomers was used to adjust these values. A series of copolymeric hydrogels with different ratios of OPGMA, 2-hydroxyethyl methacrylate (HEMA) and itaconic acid (IA) was synthesised by gamma radiation. The swelling properties were preliminarily investigated over a wide pH (2.2–9.0) and temperature (4–80 °C) ranges. Additional characterization of their structure and properties was conducted by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The presented results revealed temperature/pH dual responsive P(OPGMA/IA) and P(OPGMA/HEMA/IA) copolymers with large diversity in swelling properties, as a result of the addition of OPGMA thermoresponsive units with a lower critical solution temperature (LCST) and IA pH responsive units. It was demonstrated that VPTT can be significantly shifted to higher (e.g. body) temperatures at higher pH values (pH ≥ 4) by increasing the IA content in the hydrogel composition. Due to the possibility of making dual responsive copolymers in the manner explained in this paper, OPGMA based hydrogels show potential for different biomedical applications.