The oxidative coupling of methane to higher hydrocarbons (C2+) was studied in a bubbling fluidized bed reactor between 700°C and 820°C, and with partial pressures of methane from 40 to 70 kPa and of oxygen from 2 to 20 kPa; the total pressure was ca 100 kPa. CaO, Na2CO3/CaO and PbO/γ‐Al2O3 were used as catalytic materials. C2+ selectivity depends markedly on temperature and oxygen partial pressure. The optimum temperature for maximizing C2+ selectivity varies between 720 and 800°C depending on the catalyst. Maximum C2+ selectivities were achieved at low oxygen and high methane partial pressures and amounted to 46% for CaO (T = 780°C; PCH4 = 70 kPa; PO2 = 5 kPa), 53% for Na2CO3/CaO (T = 760°C; PCH4 = 60 kPa; PO2 = 6 kPa) and 70% for PbO/γ‐Al2O3 (T = 720°C; PCH4 = 60 kPa; PO2 = 5 kPa). Maximum yields were obtained at low methane‐to‐oxygen ratios; they amounted to 4.5% for CaO (T = 800°C; PCH4 = 70 kPa; PO2 = 12 kPa), 8.8% for Na2CO3/CaO (T = 820°C; PCH4 = 60 kPa; PO2 = 20 kPa) and 11.3% for PbO/γ‐Al2O3 (T 2= 800°C; PCH4 = 60 kPa; PO2 = 20 kPa).
In this work we describe the implementation details of a protocol suite for a secure and reliable over-the-air reprogramming of wireless restricted devices. Although, recently forward error correction codes aiming at a robust transmission over a noisy wireless medium have extensively been discussed and evaluated, we believe that the clear value of the contribution at hand is to share our experience when it comes to a meaningful combination and implementation of various multihop (broadcast) transmission protocols and custom-fit security building blocks: For a robust and reliable data transmission we make use of fountain codes a.k.a. rateless erasure codes and show how to combine such schemes with an underlying medium access control protocol, namely a distributed low duty cycle medium access control (DLDC-MAC). To handle the well known problem of packet pollution of forward-error-correction approaches where an attacker bogusly modifies or infiltrates some minor number of encoded packets and thus pollutes the whole data stream at the receiver side, we apply homomorphic message authentication codes (HomMAC). We discuss implementation details and the pros and cons of the two currently available HomMAC candidates for our setting. Both require as the core cryptographic primitive a symmetric block cipher for which, as we will argue later, we have opted for the PRESENT, PRIDE and PRINCE (exchangeable) ciphers in our implementation.
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